Daniel and Kelly’s Extraordinary Universe - Daniel answers Listener Questions about closed time-like curves, force fields, and the lifetime of the Earth's magnetic field

Episode Date: February 2, 2021

Daniel answers questions from listeners like you! Got questions? Come to Daniel's public office hours: https://sites.uci.edu/daniel/public-office-hours/ Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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so you can work, create, and boost productivity all on one device. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then everything changed. There's been a bombing at the TWA. Terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged. Terrorism.

Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back-to-school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone.

Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. So much of physics is about a journey into the impossible. We spend a lot of time in physics understanding what we see in the universe. How does the sun produce energy? Why is the universe expanding? How does light get from point A to point B? We do all this by distilling what we observe and describing it mathematically.

But there's another side to that. We can also push on the limits of what is possible to try to break down barriers and create something new that's never been. been done before. We can take our mathematical understanding of the universe and find the corners, explore the nooks and crannies, and see if we can do something that's never been done before. Truly, physics is about exploring the impossible. Hi, I'm Daniel. I'm a particle physicist. And my personal scientific fantasy is to do something people once thought was impossible. And welcome to the podcast, Daniel and Jorge explained the universe, a production of iHeartRadio, a podcast in which we explore what is possible in the universe and what might be possible and what's downright impossible. We mix it all up and we talk about it and we try to figure it out. We apply our mind. to understanding what's out there in the universe and try to bring your intuition up to speed so that

all of it makes some sense to you. And in the end, everything that we do in physics and everything that we do in science starts with a question. The question, how does that work? Or could we even do that? Or why is it this way and not that other way? And questions are wonderful because they are at the heart of science. They are the engine of our curiosity. They are the reason that science moves forward. People often think of science as this big monolithic institution that rolls forward at a steady pace year after year, but instead you should imagine it as a big swarm of people pushing with their individual little hands on some envelope, expanding the sphere of knowledge by individual effort, by curiosity, by lonely pursuits sometimes. And so it's those questions

asked by individuals that have resulted in everything we know about the universe. And that's why you should keep asking questions and you should wonder about the universe and you should put value in those questions. You should really cherish your curiosity because it's those moments of curiosity that have led us to where we are today. And that's why on this show we really value answering your questions, not just the questions that I find exciting or that Jorge is willing to talk about, but also the questions that real people are wondering about. People like you who think about the universe and wonder, how does this idea fit with that idea? Or I've heard about this a lot of times,

but I've never really understood it. So that's what we're here for to answer your questions to make sure you actually understand the universe. Hey, the name of the podcast is Explain the Universe after all. And as you might have figured out already, Jorge's not here today. So I'll be taking the opportunity to catch up on our backlog of listener questions. If you have a question about the universe, you'd like to hear us break down,

please send it to us to Questions at Danielanhorpe.com. We answer every email, we respond to every tweet, we will eventually answer your question. And some of these questions are fascinating and tricky enough that we promote them right onto the podcast and answer them directly because we think it might be a question. Lots of people are interested in hearing the answers to. So on today's program, we are tackling Listener questions about time-like curves, force fields, and the ends of the earth. Before we dig into today's questions, I want to say thank you to everybody who came to my public office hours recently.

If you have questions about the way the universe works, but you're not into writing emails and you don't tweet, and you might like to ask a follow-up question, then come hang out with me at my public office hours. You can find the instructions on my website, sites.ucy.edu slash Daniel, and you'll find directions for how to sign up for my public office hours, where I hang out with folks, talk physics, and answer questions. This last one was super fun, and I even got asked a question I had never heard before,

which for me is amazing because it means I get to think about something new. I get to put two ideas together I had never had in my head before. So, without further ado, here's our first listener question of the episode. Hi, Daniel and Jorge, I'm Autumn, and my question for you is about closed time-like curves, and what are they? I've heard a bit about them and how their solutions to the theory of general relativity, and that supposedly they allow for time travel, but other than that, not a lot. Thank you guys, and take care. All right, thank you very much, Autumn, for writing about closed-time-like curves.

this is indeed the kind of thing we like to dig into because it's something you might have heard of if you're interested in science fiction or science and time travel and all that kind of stuff because the possibility of actual time travel being allowed by the laws of physics is something that would blow our minds and hey open the possibility to fix all those mistakes you made in life so let's dig into it she asks what is a closed time-like curve and is possible to you it for time travel. Let's break it down. First, let's understand what is meant by curve in this context. Before we talk about what a closed time-like curve is, let's make sure we're using this word in a way that makes sense to everybody. When we say curve here, we don't mean the shape of

the bowl that you're eating your cereal in or the smooth shape of the surface of the earth. We're talking about something very specific. We're talking about how a particle moves through space and time. So if you imagine your head some chunk of space and there's a particle in it and that particle moves through space as time goes forward, then the path of that particle sometimes is called a world line of the particle or sometimes it's called its curve. And this is just the path of the particle as it moves through space. So that's pretty simple. Close time like curve is a special case of other kinds of curves, other kinds of world lines, paths that particles can go in. So that's what curves mean, but there's a little bit more to it because a particle has to

follow rules as it moves through space. You can't just have any curve. You can't have a curve with discontinuities in it, for example. You can't be here and then one instant later be in Andromeda. There are rules physics tells us how the present can turn into the future. And very specifically, you have a limit to where you can be in the universe based on where you are because there is a limit to the speed anything can move through the universe, which is why, of course, you can't appear in Andromeda in a moment because it's too far away. So imagine now your particle flying through space, where can it exist in the future? You can exist in the future nearby where it is, right?

Because it can move and it can move quickly, but only up to a certain speed. So this defines what we call a cone, the cone of future possibilities for where this particle can be. If it's at a certain place in a moment, then that cone is projected forward in time and tells you where it's possible to reach if you're traveling at the speed of light or less. The surface of the cone tells you where you could reach if you're traveling at the speed of light. So for example, if you move one second forward, you have a circular slice of that cone with radius of one light second. If you move one year forward, then the cone, of course, expands, and your slice of that cone is now one light year in radius. So that's why it's a cone. It starts, the tip is at you or the particle, and then it expands forward in time.

So that's the light cone. It describes all the places that you could be in the future, given that you are where you are right now. And again, the surface of the cone is as far as you could get if you're moving at the speed of light. If you're moving less than the speed of light, then of course, the number of possibilities shrinks. You can technically go anywhere in that cone if you could travel up to the speed of light. But the cone tells you sort of the maximum possible places that you can go. Now, this is important because we're talking about what's possible to do in the universe. How is it possible to move?

Can you move through space and through time? Now, in normal space, in flat space, the kind of space you imagine when you think about just space and darkness and spaceships floating out there, light cones are pretty simple. They're just cones. You're in a spaceship at a certain location. in space, then where you can go is described by your light cone. But what happens when space is weird? What happens near a massive

object? Well, then space curves and these cones get a little bit more complicated because light, for example, would change its path near a massive object. Light would change its path near a black hole. It would curve, for example. So as you get near a massive

object, your light cone is not a simple geometric cone that you would imagine. It actually bends a little it. The possible places that you could go, even if you're traveling at the speed of light, change. And this makes sense if you think about, for example, what happens near a black hole. As you get near a black hole, your cone tends to tilt towards the black hole. And eventually, once you cross the event horizon, your cone is entirely inside the black hole. That's what we mean when we say that space inside a black hole is bent so much that all of your futures,

all of your possible paths, lead towards the center of the black hole. Your entire light cone has now tilted towards the center so that every single place in that cone is now towards the singularity. So your singularity is in every possible future. There's no part of your light cone that exists outside the black hole. So it makes sense to us now to think about the trajectories of a particle. That's what we call it curve or its world line as it moves through space. And we could also imagine the possible curves for a particle, like how it might move through space. And these are dictated by the light cone, which again depends on the mass and the energy around you because that bends space itself, which is what determines the shape of this light cone. Okay. So we understand

the curve part of it. What does it mean to have a closed curve? Well, this is actually pretty simple. It just means that it turns back on itself, but not like you walk around in a circle and you're in the same location you were. Here we mean something more specific. We mean that it turns back on itself returning to the same point in space and in time. So a closed curve would be one that returns to where and when you started. How is that possible? Well, are closed timeline curves possible? It's possible if you can take these cones that we talked about and if they can tilt sort of more than 90 degrees. A light cone in flat space, if you take your units to all be one, has a 45-degree line defined by the speed of light, right?

Now, that cone tilts as you get towards a black hole so that one edge of it sort of turns more than 45 degrees, eventually towards 90 degrees. But if you built some weird thing in space, something which distorted the fabric of space so much that your light cone tilted past 90 degrees, that would open up the possibility to effectively move backwards in time. And if you had a series of these cones,

you stack them sort of on top of each other, then you could curve your world line back through time and space back to where you started. So it's essentially a circle in space time, a world line which doesn't move forward through space and time, but instead curves through space and time back to itself. And this works because if you imagine the individual particle, it can go anywhere inside its light cone, right?

That's moving into its local future. Somebody else, looking at it from the outside, remember, might have a different sense of time, and so they would see this particle moving into the past. The particle itself is always sort of experiencing its own time. Just like if you get on a spaceship and you travel really, really fast, other people might see your clocks go slow, but you experience your clock moving forward normally. In the same way, this particle would be experiencing its own normal time, but from the outside, we would see it moving backwards in time. So what is a closed time-like curve. It's a series of light cones tilted so that they loop back on themselves

and construct a path through space time that returns to the original point in time. Now, is this possible? Is this something which can actually happen? So far, we've just sort of been describing what the phrase means. We haven't worried too much about whether the laws of physics actually allow for this. So answering this question is a bit of a theoretical exploration. What we need to do is ask, is there a way to construct a universe that gives us a space time that works this way? And that's how general relativity works. General relativity describes how space and time are bent by mass and energy, and then how objects move through that bent space. So you can do it in a couple of directions. You can say, here's my mass and energy. General relativity, tell me how is

space bent. What happens to space if I have this mass and energy configuration? You can also try to go the opposite direction. You can say, hey, I'd like to have a universe that's bent in this certain way. Is that possible? Is there some way to construct a configuration of mass and energy that gives me this space? And that's tricky. These equations are always very, very hard to solve. And they've only ever been solved for a very few, very simple configurations, such as an empty, universe or a universe uniformly filled with stuff or a flat universe with a black hole in it. So it's in general very hard to solve these equations, but there was somebody who several decades ago came up with a solution that allows for closed time-like curves in general

relativity in a very weird configuration of mass and energy in the universe. So if you have an infinite spinning cylinder of dust, so something which goes on, forever and is spinning, and it's this sort of compactified collection of tiny objects, dust, basically, and it's spinning, then you could generate in space the kinds of distortions you would need to have light cones bend past 90 degrees and construct a closed time-like curve. So that's the solution in general relativity. Is it actually possible to assemble the mass in such a way that would give you those curves? We don't know.

I don't personally think it's very feasible to build an infinite spinning cylinder of dust, but it opens up the possibility. It suggests that maybe there are ways to assemble mass and energy in space so that it bends the fabric of space and time to allow for this kind of motion. Does this actually allow for time travel? Could that really happen? Well, first of all, this isn't like arbitrary time travel. It's not like back to the future, we just dial in when you want to go.

This would be a very specific path. And this object would move along this path, but it could only move along this path. It's not like you could go to any specific time or any arbitrary time. You can only move along this world line through time and space. And it would be a closed loop. So basically, you could be on it forever. You can't go back and change the past because that would be off of this closed time-like curve. And for the curve to exist, it has to reinforce itself.

It has to be a complete solution. So it doesn't allow for arbitrary time travel. But even still, wouldn't that be weird to have a particle doing a loop in space and time, even if it's stable, even if it doesn't get to go back and kill its own grandparent particle? Is that actually something which could happen on our universe? Doesn't that feel like it violates causality and all sorts of things? Well, theorists are not sure. It seems to work according to general relativity, but people suspect that in practice it probably wouldn't happen, that there's something preventing that. And we know that general relativity is a great theory. We also know it's not a perfect theory. We know that it cannot describe the universe as it is because it breaks down its

singularities like the Big Bang and the center of black holes and all sorts of crazy stuff. And so it may be that this is just an artifact of that theory, a mathematical construction which works most of the time, but sometimes gives nonsense answers. And some future theory of space time like quantum gravity would prevent this from happening. So most theorists, if you ask them, think that there's something out there that would block this from really existing. But to date, we do not know.

And our best theory about how the universe works, general relativity, which determines how space and time bend in the presence of mass does not prohibit closed time-like curves. So the jury is still out. So thanks for that awesome question, Autumn. I've been looking forward to digging into time travel and closed time-like curves. Thanks very much for sending that in. I want to get to some more questions. First, let's take a quick break.

Ah, come on, why is this taking so long? This thing is ancient. Still using yesterday's tech, upgrade to the ThinkPad X1 Carbon, ultra-light, ultra-powerful, and built for serious productivity, with Intel core ultra-processors, blazing speed, and AI-powered performance. It keeps up with your business, not the other way around. Whoa, this thing moves. Stop hitting snooze on new tech.

Win the tech search at Lenovo.com. Unlock AI experiences with the ThinkPad X1 Carp and powered by Intel Core Ultra processors so you can work, create, and boost productivity all on one device. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass.

The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is, Back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school. week on the okay story time podcast, so we'll find out soon. This person writes, my boyfriend

has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Now hold up, isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So do we find out if this person's boyfriend really cheated with his professor or not?

To hear the explosive finale, listen to the OK Storytime podcast on the Iheart Radio app, Apple Podcasts, or wherever you get your podcast. All right, we're back and we're answering questions from listeners. We talked about time travel, and now we're going to dig into something even more. more awesome and futuristic. So here's a great question about force fields. Hi, Daniel and Jorge. I have a science fiction-inspired question.

Are four fields possible, like the ones in Star Trek? Everything comes down to particles and an arrangement of them. And given that, for example, a brick wall is just a certain arrangement of particles. Could we mimic that in the air? Okay. Love this question. And mostly because I love the role of science fiction in pushing forward science in inspiring our curiosity. You know, science fiction authors are like the theorists of theorists. They think about new crazy things we might be able to do or ways the universe might work and they're not limited by mathematics or practicality or anything. And sometimes you read something that they write and you go, hmm, I wonder if that is possible. Maybe we could actually do that. And so thank you, science fiction authors for injecting crazy ideas into the minds of everybody out there and being on the vanguard of creative thinking. So this,

question is about force fields. Could we build force fields? First of all, we have to talk about what we mean by a force field. And if I was going to commission a force field for my spaceship, for example, because I was about to go into intergalactic war or whatever, here's what I would want. I would want it to be invisible, or at least mostly invisible, because I want to be able to see through it. I have a spaceship, for example, and a force field around it, I don't want turning on the force field to mean that I can't see anything outside in the universe. Then I'd be a huge strategic disadvantage. So it should be invisible or at least translucent.

And then it should block weapons, right? It should be able to absorb radiation weapons like lasers. And it should be able to stop matter weapons like kinetic energy weapons, you know, bullets or other kind of momentum driven weapons. So that's what I'd like. And you know, as a bonus, it'd be cool if it could, for example, be used to hold prisoners, right? You could like trap somebody who you've captured and put them in the hold of your ship and use

a force field so you didn't have to build. cells and easily configure it and all this kind of stuff. So that's my wish list for a force field. It should be invisible. It should be able to block radiation weapons and it should be able to block matter weapons. And if possible, you should also be able to touch it without actually being damaged. And that's a long list of requirements. So let's talk about what is actually possible and what might be possible in terms of force fields. So I did a little bit of research in this. And there are people out there actually doing research on force fields. Some of the things don't seem like the kind of force fields we're talking about. For example, there's a company out there

building electric armor. The idea here is to turn the skin of your spaceship or your tank or whatever into something which responds to a bullet. So if somebody shoots a bullet at you, it's not just an inner wall of matter, which absorbs that energy and maybe gets destroyed, but it responds to it. So the way they do this is by making two layers of armor and having a huge electrical gap between them. And when something impacts on that armor, it basically closes that gap and results in a huge electric discharge which pushes back on the bullet. It's sort of reactive armor, which responds when you're hit with a force backwards. So that's pretty cool, but it's not really a force field. I mean, it's not invisible. You'd need to build it. You couldn't like turn it on or off and only works on

matter weapons. It doesn't stop lasers, for example. But, you know, it's something that people are actually doing. And so it's something you might actually see out there in the world. soon. But let's talk about what might be possible. You know, when I think about a force field, first I think about the Earth's force fields because the Earth actually does have a force field. We have a huge magnetic field that protects the Earths from particles. The big swirling masses of melted rock and metal in the core of the Earth are providing an enormous magnetic engine, which creates a huge magnetic field with sort of vertical field lines that go from the north to the south or the south to the north. And what this does is when charged particles

hit a magnetic field, they get curved, right? This is the Lorentz law in physics. And so an electron, for example, generated in the sun and given a huge amount of energy and shot towards the earth, which might otherwise penetrate through the atmosphere and give you cancer, instead is bent around these magnetic field lines and funneled up to the north pole or down to the south pole. So that's cool because it's real and it exists. It doesn't really satisfy all of our requirements. I mean, it is invisible and it can deflect matter, but with a couple of big caveats, like it only works on charged particles, right? It works on electrons, works on protons. It does not work on neutral particles because neutral particles don't feel those magnetic fields. It depends on the charge of the

particle. Remember that electricity and magnetism are very tightly woven together. They're actually just two sides of the same coin. So these magnetic fields only deflect charge particles. Plus, they don't really deflect it. They just sort of focus it on their normal. pole and the South Pole. People think, wow, Aurora Borealis is really cool. It's cool, but it's radiation. So if you live near the North Pole or the South Pole, you actually get more cosmic radiation than anywhere else on Earth because the magnetic field sort of funnels it up there and funnels it down to the South Pole. So it's protecting the rest of the Earth, but at the expense of the North and the Southern Caps. So not even really deflecting those charged particles. And then,

of course, it doesn't work on radiation. A magnetic field will not stop a laser. beam. A laser beam is made of photons and photons don't feel magnetic fields, which you know is kind of weird because photons are partially magnetic fields. They are oscillating electromagnetic waves, right? The electrical component oscillating into the magnetic component and then back, but photons are neutral. They have no electric charge. And so again, they are not deflected by magnetic fields. So a magnetic field, kind of like a force field, but not really. And also kind of impractical. If you wanted to have a really powerful magnetic force field, you need to be able to generate that inside your spaceship. You don't really want to have enormous massive currents of iron and nickel

sloshing around in the inside of your spaceship to generate this magnetic field. All right. So what else could we do? Well, the third possibility is a plasma shield. Plasma is another state of matter. Basically, you just take gas and you make it even hotter. Then the electrons have so much energy that they whizz off, they leave their protons, and now they're free. So it's ionized gas. You take all the atoms and gas and you break apart the electrons and the nuclei, and that's what a plasma is. It's nothing special or fancy or science fictiony. It's just gas that's been heated up so much that the electrons now run free. But it is super duper hot and it's electrically charged. And that means it has the capability to basically vaporize anything. I mean, imagine basically a slice of the sun. The sun is

plasma. It's super duper hot and it's ionized. So imagine, for example, having a shield around your spaceship that was a slice of the sun. You threw anything in it, boom, it would melt. Also, it's opaque to lasers, right? A laser can't penetrate the sun because it's filled with charged particles which would interact with the light in the laser. Unless, of course, you tune the laser to be a specific frequency that the plasma didn't absorb. But these excited particles, these free particles, are not limited to absorbing only very specific frequencies. So it would be very difficult to get your laser beam through a slice of the sun, through a plasma shield.

So that's pretty cool. And actually, we have a little bit of a plasma shield already on Earth. The part of the atmosphere we call the ionosphere is basically plasmas filled with ions. And it blocks a lot of radiation from the sun, neutral radiation, photons, etc. And our ionosphere is not very dense, so mostly blocks very long wavelength radiation.

But if you made a denser plasma more like a slice of the sun, then you could block shorter wavelengths. So this is the kind of thing you could actually build. Now, how do you make a plasma shield? How is that possible? Can you actually do that? It would be pretty tricky. I mean, you need to have basically a shell of gas. And then you need to have that gas get excited.

Get very, very hot. You need to dump a huge amount of energy into it. So you can imagine, for example, puffing out a shell of gas and then zapping it with a bunch of lasers to turn. it into a plasma shield, like essentially deposit so much energy in this shield around you that anything else that comes into it would get absorbed or interacted with or diffused. This is not something that's very easy to do, not something we have the technology to do at all. Already it's difficult for us to make and control plasmas. This essentially is the task of fusion. We are trying to replicate what's happening on the sun in laboratories on Earth, not just so we can build

forest fields, but so that we can generate essentially limitless energy through nuclear fusion, the same process that happens in the center of the sun. And it's tricky. People have been working on it for decades. They're trying to make a donut of plasma and they're containing it with magnetic fields because the stuff is so volatile. It would vaporize any container you put it in. It's so hot and nasty and interactive. So they use a magnetic bottle to contain this plasma. They have basically a donut of the sun and it's hard to get it to go. It's hard to keep it straight. This is a big engineering challenge and there's a project going on right now called Eater, which is the biggest and very promising application of this, but it costs billions of dollars and it's not simple

to set up. So this would be a very difficult engineering challenge and you'd have to somehow create this shield around your spaceship, get it zapped up to turn it into a plasma and then keep it in line with very strong magnets. So possibly you could do that potentially sometime in the future. It might be possible, but it sort of violates one of the first principles we asked for for a force field, which is that it's invisible. If you surrounded yourself with sort of a sheet of the sun in a sphere around your ship, then you wouldn't be able to see anything outside that sphere and you'd be stuck inside basically a little slice of the sun, which I guess would get pretty hot. So that's sort of the best idea that's out there that I'm aware of to build an actual force field, but it has a lot

of engineering challenges ahead of it. And even if we could solve all of those, it doesn't actually satisfy all the requirements we have. So fun question, maybe somebody in the future will come up with a new way to think about how to actually build a force field. And that shouldn't stop anybody from imagining and from wondering and from being creative. So keep using force fields in the science fiction that you write and keep an eye out in science fiction for other cool ideas that we might actually turn one day into reality. All right. I want to get to one more question, but first, let's take another break. Ah, come on. Why is this taking so long? This thing is ancient.

Still using yesterday's tech, upgrade to the ThinkPad X1 Carbon, Ultra Light, Ultra Powerful, and built for serious productivity with Intel Core Ultra processors, blazing speed, and AI power performance. It keeps up with your business, not the other way around. Whoa, this thing moves. Stop hitting snooze on new tech. Win the Tech Search at Lenovo. Lenovo.com. Unlock AI experiences with the ThinkPad X1 Carbon, powered by Intel Core Ultra processors, so you can work, create,

and boost productivity all on one device. December 29th, 1975, LaGuardia Airport. The holiday rush. Parents hauling luggage, kids gripping their new Christmas toys. Then, At 6.33 p.m., everything changed. There's been a bombing at the TWA terminal.

Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. Season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart

Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OKStrees. Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone.

Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet.

So do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. All right, we are back and we are having a lot of fun talking about the future and time travel and force fields and future technologies. And now I want to take a trip even deeper into the future. wondering how long humans can survive on Earth. Hi, Daniel and Jorge. My name is Gavin, and I live in South Wales in the United Kingdom. In the last podcast, What's Inside the Earth?

You got me thinking, you told us that the big lump of moon-sized core inside the Earth is getting bigger by one millimeter every year and that at some point in the future, the core will stop turning and the Earth will lose its magnetic force, like we think, happen to Mars. My question is, will this happen before our sun goes supernova? All right. Thank you very much for that question.

And also, on behalf of all of humanity, thank you so much for thinking ahead, for worrying because we don't have time to about the deep future and starting to make plans today for what we might have to do to prepare for it. So he's wondering which of these two calamities will we have to deal with first, the sun exploding and fizzling out or the Earth's magnetic. field dying. And the two are related, of course, because the earth magnetic field is important for protecting us from the sun's radiation. So if it disappears, then we will be fried. But hey, if it's going to last longer than the sun, then we don't need to worry about it. So which one will kill us first is basically the name of the game in this question. So first let's remind ourselves what the timeline is for our sun. How long is this thing going to keep burning and keeping us toasty and keeping us keeping on. So our sun is currently about 5 billion years old. It's about the age of the solar

system because it basically is the solar system. Remember that it coalesced together from a huge cloud of gas and dust and leftovers from population 3 and population 2 stars and gathered together in some gravitational event slowly slurping together and that most of the stuff in the solar system is in the sun. About 99% of everything that's in the solar system is the sun. So we're just like a little detail on top of the sun. Now, that happened about four and a half to five billion years ago. And since then, what's the sun been doing? Well, it's been burning hydrogen. Gravity gathers together all this material, mostly hydrogen, but also some helium left over from burning from previous generations and a few other heavier elements, but still overwhelmingly hydrogen.

And that's good because that's the fuel for the sun. Gravity squeezes together this hydrogen. And it gets it close enough, then it can fuse. Remember that hydrogen is essentially just a proton with an electron around it. But when things get hot, it's basically just a proton. And to make fusion happen, you've got to squeeze two of these protons together. But protons are both positively charged, and so they resist. And until you get them closed enough together, when the strong force can take over and do nuclear fusion and release a bunch of energy, they will resist. And that's why fusion is hard to make happen. You need really high temperatures and pressures. That's why it's difficult for them to engineer it here on Earth.

But anyway, it happens in the sun and it's been happening now for about 5 billion years. So what's going to keep the sun from burning on forever? Well, eventually it's going to run out of fuel. It's basically a huge hydrogen thermonuclear device. And what happens when it burns hydrogen is that it creates ash. That ash is helium. And it starts at the core because that's where in the fusion starts. That's the hottest, densest part.

So hydrogen first burns out at the core. And you get this helium core now surrounded by hydrogen, and the fusion is now happening in the sort of outer layers surrounding the core. This pushes out on the sun, making it bigger and bigger, it fluffs it out larger and larger, and actually even makes it brighter and brighter. So every year, the sun gets a little bit hotter. In four billion years, for example, the sun will be about 40% brighter than it is today. And just that is enough to like boil all of the oceans on Earth and turn them into vexed. So right there, you can see that in about four billion years, our sun will not make Earth a very cozy place to live in. But as the sun grows, it's going to get bigger and bigger. You might think,

well, how much bigger can it get? It's already huge, right? It's already a million times the volume of the Earth. Well, it's going to get bigger by a lot. It's going to grow by about a factor of 200. And that's bad news because it means it's going to get so big that its radius is going to match the size of Earth's orbit. Right. It's going to envelop all. all the inner planets and the earth will be right there, right about on the edge of the sun. What does that mean to be like inside the sun or right just past the edge of the sun? Well, it's going to be really hot and we're going to be surrounded by these huge sheaves of burning hydrogen, which is not going to be a good place to live in.

Now, inside the sun, you now have a helium core, which is getting bigger and bigger because as hydrogen burns, it creates more and more helium. And eventually, you can even fuse this helium together to make something even heck. heavier carbon. And so this is awesome because it burns hydrogen for millions and millions and billions of years. And then all of a sudden it starts to burn helium. It passes this critical point and you get this helium flash. And the amount of energy generated by the sun in this moment is actually brighter than all the stars in the galaxy put together. Although you don't get to see it because it's absorbed by the inner layers of the sun. But maybe that's good because otherwise it would

fry everything on Earth. So it starts helium fusion, creating carbon. And our sun is not heavy enough. It's not massive enough to then take the next step and fuse carbon into heavier elements. You could eventually make oxygen and neon and silicon and all sorts of crazy stuff if you had a bigger star. Our star is not big enough to do that. So what's going to happen is it's going to accumulate helium, which will burn into carbon, but then it's sort of stuck there. The carbon is inert. And it's like having a lot of ash in your fire.

It makes it harder for things to burn. And so the sun will just sort of decrease in brightness from there. basically fizzling out and turning into a white dwarf. A white dwarf is just a hot blob of carbon. It's not fusing anymore. It's not producing any more energy, but it's still really, really hot. It glows. White dwarfs are called white because they do give off light. Again, not because they're actually fusing, they're creating new energy. They're just glowing the same way that anything that's hot glows. It's a white, hot lump of carbon in the universe and so it glows white, the way like a really hot, piece of metal that you stick into a blacksmith's furnace will also glow white hot.

And eventually it will cool. And scientists think that white dwarfs, if given enough time, will eventually radiate off all of their energy and turn into something else, something weird, something called a cold black dwarf. But that will take trillions of years. So let's review the timeline. We're about 5 billion years into the life cycle of the sun. It will keep burning for about 5 billion more years, after which it will be able to.

will envelop the earth, will have the helium flash, and it'll convert into a white dwarf, which won't give off enough heat to keep the earth warm, but the earth will have already been fried at that point. And then eventually the white dwarf in trillions of years will cool off. So timeline for the sun to fry us is a few billion years. Now let's turn to the other side of the question. How long will we have a magnetic field for? To answer this question, we need to think about what causes the magnetic field and why that might come to an end. So as we talked about a few minutes ago, the magnetic field, we think, comes from internal flows of molten rock and metal. And again, it's good idea to sort of turn back at the clock and remember how the earth

was formed and why it is the way it is. We think the earth came together, basically a bunch of bits of rock, which gathered together into larger bits of rock, into larger bits of rock. So the early earth was just a collection of rock basically squeezed together and it wasn't actually melted in the middle yet. Gravity then took over and squeezed it further and further. that plus radioactive decay from certain heavy metals that were embedded in the rock helped melt the center of the earth.

This might have taken a few hundred million years to melt the center of the earth, to make it molten rather than just hot rock. And this was crucial because it let all the heavy elements, the iron, the nickel sort of melt down. Things get hot, they get molten, they get liquid. Now you have a fluid instead of rock. So it's easier for things to sort of like slide around and rearrange themselves. So the heavier elements sync to the core, and now you get the structure that we have today,

which is a solid inner core, very, very dense, surrounded by that liquid outer core, and then on top of that is the mantle, which isn't exactly liquid, but it is rock that's sort of flowing, and then on top of that is the crust, the thing that we actually live on. And we think that it's this molten motion inside the earth, essentially this liquid outer core that's generating the magnetic field, that it's spinning, that there's electric currents in there, and that motion of electric charges creates magnetic fields. Because remember, there's a very tight connection between electricity and magnetism. There really are just one thing, electromagnetism, which is why moving particles can generate magnetic fields

and why magnetic fields can bend the path of charged particles. So what happens is this stuff is swirling around. It's basically a current and that creates a magnetic field. And that magnetic field enhances the current, right? The magnetic field pushes these particles in a circle. And then moving in a circle makes a bigger magnetic field. This is called a dynamo effect basically builds on itself and makes a stronger and stronger magnetic field.

But it relies on the flowing of this liquid molten rock and metal in the center of the earth. Outside the inner core, you have to have the ability for this thing to slosh around. You need the motion in order to have a magnetic field. And as the question mentioned, this inner core is growing. The earth is cooling. Basically, it's freezing very slowly. And this core is growing by one millimeter per year. And that's just because things cool, right?

We are giving off heat into space the same way that a white dwarf will eventually radiate out all of its energy into space and become a cold black dwarf. Entropy tells us that heat should spread out. So you have an isolated, hot blob of something in cold space. Eventually it will radiate out its energy. So that's what's happening to Earth. And the inner core is growing. And eventually it will grow and it will cool down the earth.

So how long will this take? Will it be faster than the sun enveloping the earth and frying us, or will it be slower? It's difficult to predict these things because it requires projecting out pretty far in time and our understanding of how these things work inside the earth is still a little speculative. We've never drilled down to the earth. A lot of this stuff is reconstructed from seismographs, from basically bouncing waves off the inside of the earth and understanding how those waves are reflected as they hit various layers inside the earth. So there's still a lot of guesswork involved, but the best estimate I found is that it will take about 90 billion years for the Earth to lose this magnetic field.

Essentially, for the Earth to freeze internally and to stop having the flowing liquid rock and metal necessary to have a magnetic field. So that's 91 billion years. That's a lot longer than the Sun's expected lifetime. The Sun we think will fizzle out in about 5 billion years. So the Earth, if it survives that, if it doesn't just get like melted and slurped into the sun, would continue on for a long time for tens of billions of years with a magnetic field, spinning and reflecting charged particles happily, even if we're now orbiting a white dwarf.

So we think the sun will expand and it'll fry the Earth in a few billion years, after which it'll collapse to a white dwarf, and then the Earth with its magnetic field will orbit this white dwarf for billions of years until eventually it cools and solidifies and loses its magnetic field in something like 90 billion years. So that's definitely something to think about, something to plan for, something to wonder about. I think personally, we'd be lucky if we made it a billion years on this Earth so that we

had to worry about things like the sun getting bigger and frying us. We have more immediate problems that we need to tackle, not force fields, not close time-like curves, but just sort of taking care of the planet so we can last that long. Anyway, it's fun to think about these things and fun to understand the physics that goes into making a sun or making a magnetic field so that you can understand how long they will last. All right, thanks everybody for sending in these questions and for letting us ride with you on your curiosity journey, for wondering about the nature of space, for wondering if it's possible to go backwards in time, to build force fields, and how long this planet Earth will be around for us to live on. It's a joy to get your emails and a joy to think about the ideas that. in your head. So please don't be shy. Send us your questions. Tune in next time. Ah, come on, why is this taking so long?

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Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys, then everything changed. It's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious.

Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.

Thank you.