Latest / 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

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

• 0:08
  Speaker 1: So much of physics is about a journey into the impossible.
• 0:12
  Speaker 1: We spend a lot of time in physics understanding what
• 0:15
  Speaker 1: we see in the universe. How does the Sun produce energy,
• 0:19
  Speaker 1: Why is the universe expanding? How does light get from
• 0:22
  Speaker 1: point A to point B. We do all this by
• 0:24
  Speaker 1: distilling what we observe and describing it mathematically. But there's
• 0:28
  Speaker 1: another side to that. We can also push on the
• 0:32
  Speaker 1: limits of what is possible to try to break down
• 0:35
  Speaker 1: barriers and create something new that's never been done before.
• 0:39
  Speaker 1: We can take our mathematical understanding of the universe and
• 0:43
  Speaker 1: find the corners, explore the nooks and crannies, and see
• 0:47
  Speaker 1: if we can do something that's never been done before. Truly,
• 0:51
  Speaker 1: physics is about exploring the impossible. Hi, I'm Daniel. I'm
• 1:11
  Speaker 1: a particle physicist and my personal scientific fantasy is to
• 1:15
  Speaker 1: do something people once thought was impossible. And Welcome to
• 1:20
  Speaker 1: the podcast Daniel and Jorgey Explain the Universe, a production
• 1:25
  Speaker 1: of I Heart Radio, a podcasting which we explore what
• 1:28
  Speaker 1: is possible in the universe and what might be possible
• 1:31
  Speaker 1: and what's downright impossible. We mix it all up and
• 1:35
  Speaker 1: we talk about it. We try to figure it out.
• 1:37
  Speaker 1: We apply our minds to understanding what's out there in
• 1:41
  Speaker 1: the universe and try to bring your intuition up to
• 1:44
  Speaker 1: speed so that all of it makes some sense to you.
• 1:47
  Speaker 1: And in the end, everything that we do in physics,
• 1:50
  Speaker 1: and everything that we do in science starts with a question,
• 1:53
  Speaker 1: the question how does that work? Or could we even
• 1:56
  Speaker 1: do that? Or why is it this way and not
• 1:59
  Speaker 1: the other way? And questions are wonderful because they are
• 2:03
  Speaker 1: at the heart of science. They are the engine of
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  Speaker 1: our curiosity. They are the reason that science moves forward.
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  Speaker 1: People often think of science as this big, monolithic institution
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  Speaker 1: that rolls forward at a steady pace year after year.
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  Speaker 1: But instead you should imagine it as a big swarm
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  Speaker 1: of people pushing with their individual little hands on some envelope,
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  Speaker 1: expanding the sphere of knowledge by individual effort, by curiosity,
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  Speaker 1: by lonely pursuits sometimes. And so it's those questions asked
• 2:32
  Speaker 1: by individuals that have resulted in everything we know about
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  Speaker 1: the universe. And that's why you should keep asking questions,
• 2:39
  Speaker 1: and you should wonder about the universe, and you should
• 2:42
  Speaker 1: put value in those questions. You should really cherish your
• 2:46
  Speaker 1: curiosity because it's those moments of curiosity that have led
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  Speaker 1: us to where we are today. And that's why on
• 2:52
  Speaker 1: this show we really value answering your questions, not just
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  Speaker 1: the questions that I find exciting or the whore he
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  Speaker 1: is willing to talk out, but also the questions that
• 3:01
  Speaker 1: real people are wondering about, people like you who think
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  Speaker 1: about the universe and wonder how does this idea fit
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  Speaker 1: with that idea or I've heard about this a lot
• 3:10
  Speaker 1: of times, but I've never really understood it. So that's
• 3:13
  Speaker 1: what we're here for, to answer your questions, to make
• 3:15
  Speaker 1: sure you actually understand the universe. Hey, the name of
• 3:19
  Speaker 1: the podcast is Explain the Universe after all. And as
• 3:23
  Speaker 1: you might have figured out already, Jorge is not here today,
• 3:25
  Speaker 1: so I'll be taking the opportunity to catch up on
• 3:28
  Speaker 1: our backlog of listener questions. If you have a question
• 3:32
  Speaker 1: about the universe you'd like to hear us break down,
• 3:34
  Speaker 1: please send it to us two questions at Daniel and
• 3:37
  Speaker 1: Jorge dot com. We answer every email, we respond to
• 3:40
  Speaker 1: every tweet. We will eventually answer your question. And some
• 3:44
  Speaker 1: of these questions are fascinating and tricky enough that we
• 3:47
  Speaker 1: promote them right onto the podcast and answer them directly
• 3:51
  Speaker 1: because we think it might be a question lots of
• 3:53
  Speaker 1: people are interested in hearing the answers to, so on
• 3:57
  Speaker 1: today's program, we are tackling listener questions about time like curves,
• 4:06
  Speaker 1: force fields, and the ends of the Earth. Before we
• 4:10
  Speaker 1: dig into today's questions, I want to say thank you
• 4:12
  Speaker 1: to everybody who came to my public office hours recently.
• 4:16
  Speaker 1: If you have questions about the way the universe works,
• 4:18
  Speaker 1: if you're not into writing emails and you don't tweet,
• 4:21
  Speaker 1: and you might like to ask a follow up question,
• 4:23
  Speaker 1: then come hang out with me at my public office hours.
• 4:26
  Speaker 1: You can find the instructions on my website sites dot
• 4:29
  Speaker 1: U c I, dot E, d U slash Daniel, and
• 4:31
  Speaker 1: you'll find directions for how to sign up for my
• 4:33
  Speaker 1: public office hours, where I hang out with folks, talk
• 4:36
  Speaker 1: physics and answer questions. This last one was super fun
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  Speaker 1: and I even got asked a question I had never
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  Speaker 1: heard before, which for me is amazing because it means
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  Speaker 1: I get to think about something new. I get to
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  Speaker 1: put two ideas together I had never had in my
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  Speaker 1: head before. So, without further ado, here's our first listener
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  Speaker 1: question of the episode. Hi Daniel and Horror. Hey, I'm Autumn,
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  Speaker 1: and my question for to you is about closed time
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  Speaker 1: like curves and what are they. I've heard a bit
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  Speaker 1: about them and how their solutions to the theory of
• 5:08
  Speaker 1: general relativity, and that supposedly they allow for time travel,
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  Speaker 1: but other than that not a lot. Thank you guys,
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  Speaker 1: and take care all right. Thank you very much Autumn
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  Speaker 1: for writing about closed timelike curves. This is indeed the
• 5:24
  Speaker 1: kind of thing we like to dig into because it's
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  Speaker 1: something you might have heard of if you're interested in
• 5:29
  Speaker 1: science fiction or science and time travel and all that
• 5:33
  Speaker 1: kind of stuff. Because the possibility of actual time travel
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  Speaker 1: being allowed by the laws of physics is something that
• 5:39
  Speaker 1: would blow our minds and hey open the possibility to
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  Speaker 1: fix all those mistakes you made in life. So let's
• 5:46
  Speaker 1: dig into it. She asks, what is a closed timelike
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  Speaker 1: curve and is it possible to use it for time travel?
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  Speaker 1: Let's break it down first. Let's understand what is meant
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  Speaker 1: by curve in this context before we talk about what
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  Speaker 1: a closed timelike curve is. Let's make sure we're using
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  Speaker 1: this word in a way that makes sense to everybody.
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  Speaker 1: When we say curve here, we don't mean the shape
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  Speaker 1: of the bowld you're eating your cereal in, or the
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  Speaker 1: smooth shape of the surface of the Earth. We're talking
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  Speaker 1: about something very specific. We're talking about how a particle
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  Speaker 1: moves through space and time. So if you imagine your head,
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  Speaker 1: some chunk of space, and there's a particle in it,
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  Speaker 1: and that particle moves through space as time goes forward,
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  Speaker 1: then the path of that particle sometimes it's called a
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  Speaker 1: worldline of the particle, or sometimes it's called it's curve,
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  Speaker 1: and this is just the path of the particle as
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  Speaker 1: it moves through space. So that's pretty simple, closed timelike
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  Speaker 1: curves a special case of other kinds of curves, other
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  Speaker 1: kinds of worldlines, paths that particles can go in. So
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  Speaker 1: that's what curves mean. But there's a little bit more
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  Speaker 1: to it, because a particle has to follow rules as
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  Speaker 1: it moves through space. You can't just have any curve.
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  Speaker 1: You can't have a curve with discontinuities in it. For example,
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  Speaker 1: you can't be here and then one instant later be
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  Speaker 1: an Andromeda. There are rules. Physics tells us how the
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  Speaker 1: present can turn into the future, and very specifically, you
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  Speaker 1: have a limit to where you can be in the
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  Speaker 1: universe based on where you are, because there is a
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  Speaker 1: limit to the speed anything can move through the universe,
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  Speaker 1: which is why, of course, you can't appear in Andromeda
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  Speaker 1: in a moment because it's too far away. So imagine
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  Speaker 1: now your particle flying through space. Where can it exist
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  Speaker 1: in the future. You can exist in the future nearby
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  Speaker 1: where it is right, because it can move, and it
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  Speaker 1: can move quickly, but only up to a certain speed.
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  Speaker 1: So this defines what we call a cone, the cone
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  Speaker 1: of future possibilities for where this particle can be. If
• 7:50
  Speaker 1: it's at a certain place in a moment, then that
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  Speaker 1: cone is projected forward in time and tells you where
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  Speaker 1: it's possible to reach if you're traveling at the speed
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  Speaker 1: of light or less. The surface of the cone tells
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  Speaker 1: you where you could reach if you're traveling at the
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  Speaker 1: speed of light. So, for example, if you move one
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  Speaker 1: second forward, you have a circular slice of that cone
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  Speaker 1: with radius of one light second. If you move one
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  Speaker 1: year forward, then the cone, of course expands and your
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  Speaker 1: slice of that cone is now one light year in radius.
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  Speaker 1: So that's why it's a cone. It starts the tip
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  Speaker 1: is at you or the particle, and then it expands
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  Speaker 1: forward in time. So that's the light cone. It describes
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  Speaker 1: all the places that you could be in the future,
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  Speaker 1: given that you are where you are right now. And again,
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  Speaker 1: the surface of the cone is as far as you
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  Speaker 1: could get if you're moving at the speed of light.
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  Speaker 1: If you're moving less than the speed of light, then
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  Speaker 1: of course the number of possibilities shrinks. You can technically
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  Speaker 1: go anywhere in that cone if you could travel up
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  Speaker 1: to the speed of light, but the cone tells you
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  Speaker 1: sort of the maximum possible places that you can go.
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  Speaker 1: And this is important because we're talking about what's possible
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  Speaker 1: to do in the universe. How is it possible to move?
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  Speaker 1: Can you move through space and through time? Now in
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  Speaker 1: normal space and flat space, the kind of space you
• 9:03
  Speaker 1: imagine when you think about just space and darkness and
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  Speaker 1: spaceships floating out there. Light cones are pretty simple, and
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  Speaker 1: they're just cones. You're in a spaceship, but a certain
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  Speaker 1: location in space, then where you can go is described
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  Speaker 1: by your light cone. But what happens in space is weird.
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  Speaker 1: What happens near a massive object, well, then space curves
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  Speaker 1: and these cones get a little bit more complicated because light,
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  Speaker 1: for example, would change its path near a massive object,
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  Speaker 1: light would change its path. Near a black hole, it
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  Speaker 1: would curve, for example, So as you get near a
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  Speaker 1: massive object, your light cone is not a simple geometric
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  Speaker 1: cone that you would imagine. It actually bends a little
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  Speaker 1: bit the possible places that you could go, even if
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  Speaker 1: you're traveling at the speed of light change. And this
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  Speaker 1: makes sense if you think about, for example, what happens
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  Speaker 1: near a black hole. As you get near a black hole,
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  Speaker 1: your cone tends to tilt towards the black hole, and eventually,
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  Speaker 1: once you cross the event horizon, your cone isn't higherly
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  Speaker 1: inside the black hole. That's what we mean when we
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  Speaker 1: say that space inside a black hole is bent so
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  Speaker 1: much that all of your futures, all of your possible paths,
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  Speaker 1: lead towards the center of the black hole. Your entire
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  Speaker 1: light cone has now tilted towards the center, so that
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  Speaker 1: every single place in that cone is now towards the singularity.
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  Speaker 1: So your singularity is in every possible future. There's no
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  Speaker 1: part of your light cone that exists outside the black hole.
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  Speaker 1: So it makes sense to us now to think about
• 10:28
  Speaker 1: the trajectories of a particle. That's what we call its
• 10:30
  Speaker 1: curve or its worldline as it moves through space. And
• 10:33
  Speaker 1: we can also imagine the possible curves for a particle,
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  Speaker 1: like how it might move through space, and these are
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  Speaker 1: dictated by the light cone, which again depends on the
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  Speaker 1: mass and the energy around you, because that bends space itself,
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  Speaker 1: which is what determines the shape of this light cone. Okay,
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  Speaker 1: so we understand the curve part of it. What does
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  Speaker 1: it mean to have a closed curve? Well, this is
• 10:55
  Speaker 1: actually pretty simple. It just means that it turns back
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  Speaker 1: on itself. But not like you walk around in a
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  Speaker 1: circle and you're in the same location you were here.
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  Speaker 1: We mean something more specific. We mean that it turns
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  Speaker 1: back on itself, returning to the same point in space
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  Speaker 1: and in time. So a closed curve would be one
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  Speaker 1: that returns to where and when you started. How is
• 11:19
  Speaker 1: that possible? Well, are closed time like curves possible? It's
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  Speaker 1: possible if you can take these cones that we talked about,
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  Speaker 1: and if they can tilt sort of more than ninety degrees.
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  Speaker 1: A light cone in flat space, if you take your
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  Speaker 1: units to all be one, has a forty five degree
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  Speaker 1: line defined by the speed of light. Right now, that
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  Speaker 1: cone tilts as you get towards a black hole, so
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  Speaker 1: that one edge of it sort of turns more than
• 11:45
  Speaker 1: forty five degrees eventually towards ninety degrees. But if you
• 11:49
  Speaker 1: built some weird thing in space, something which distorted the
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  Speaker 1: fabric of space so much that your light cone tilted
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  Speaker 1: past ninety degrees, that would open up the possibility to
• 11:59
  Speaker 1: effect really move backwards in time. And if you had
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  Speaker 1: a series of these cones, you stack them sort of
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  Speaker 1: on top of each other, then you could curve your
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  Speaker 1: worldline back through time and space back to where you started.
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  Speaker 1: So it's essentially a circle in space time, a worldline
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  Speaker 1: which doesn't move forward through space and time, but instead
• 12:19
  Speaker 1: curves through space and time back to itself. And this
• 12:23
  Speaker 1: works because if you imagine the individual particle, it can
• 12:26
  Speaker 1: go anywhere inside its light cone. Right that's moving into
• 12:30
  Speaker 1: its local future. Somebody else looking at it from the outside, remember,
• 12:35
  Speaker 1: might have a different sense of time, and so they
• 12:37
  Speaker 1: would see this particle moving into the past. The particle
• 12:40
  Speaker 1: itself is always sort of experiencing its own time. Just
• 12:44
  Speaker 1: like if you get on a spaceship and you travel
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  Speaker 1: really really fast. Other people might see your clocks go slow,
• 12:49
  Speaker 1: but you experience your clock moving forward normally in the
• 12:52
  Speaker 1: same way, this particle would be experiencing its own normal time,
• 12:57
  Speaker 1: but from the outside we would see it moving back
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  Speaker 1: words in time. So what is a closed time like curve.
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  Speaker 1: It's a series of light cones tilted so that they
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  Speaker 1: loop back on themselves and construct a path through space
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  Speaker 1: time that returns to the original point in time. Now,
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  Speaker 1: is this possible? Is this something which can actually happen?
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  Speaker 1: So far we've just sort of been describing what the
• 13:20
  Speaker 1: phrase means. We haven't worried too much about whether the
• 13:23
  Speaker 1: laws of physics actually allow for this, So answering this
• 13:26
  Speaker 1: question is a bit of a theoretical exploration. What we
• 13:29
  Speaker 1: need to do is ask is there a way to
• 13:32
  Speaker 1: construct a universe and gives us a space time that
• 13:36
  Speaker 1: works this way? And that's how general relativity works. General
• 13:40
  Speaker 1: relativity describes how space and time are bent by mass
• 13:45
  Speaker 1: and energy, and then how objects move through that bent space.
• 13:50
  Speaker 1: So you can do it in a couple of directions.
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  Speaker 1: You can say, here's my mass and energy. General relativity
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  Speaker 1: tell me how is space bent? What happens to space?
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  Speaker 1: If I have this mass and energy configuration. You can
• 14:02
  Speaker 1: also try to go the opposite direction. You could say, hey,
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  Speaker 1: I'd like to have a universe that's bent in this
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  Speaker 1: certain way. Is that possible? Is there some way to
• 14:12
  Speaker 1: construct a configuration of mass and energy that gives me
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  Speaker 1: this space? And that's tricky. These equations are always very
• 14:19
  Speaker 1: very hard to solve, and they've only ever been solved
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  Speaker 1: for a very few very simple configurations, such as an
• 14:26
  Speaker 1: empty universe or a universe uniformly filled with stuff, or
• 14:31
  Speaker 1: a flat universe with a black hole in it. So
• 14:33
  Speaker 1: it's in general very hard to solve these equations. But
• 14:37
  Speaker 1: there was somebody who several decades ago came up with
• 14:40
  Speaker 1: a solution that allows for closed time like curves. In
• 14:45
  Speaker 1: general relativity in a very weird configuration of mass and
• 14:49
  Speaker 1: energy in the universe. So if you have an infinite
• 14:53
  Speaker 1: spinning cylinder of dust to something which goes on forever
• 14:57
  Speaker 1: and is spinning, and it's this sort of compactified collection
• 15:01
  Speaker 1: of tiny objects dust basically, and it's spinning, then you
• 15:05
  Speaker 1: could generate in space the kinds of distortions you would
• 15:09
  Speaker 1: need to have light cones bend past ninety degrees and
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  Speaker 1: construct a closed time like curve. So that's the solution.
• 15:17
  Speaker 1: In general relativity is it actually possible to assemble the
• 15:21
  Speaker 1: mass in such a way that would give you those curves.
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  Speaker 1: We don't know. I don't personally think it's very feasible
• 15:27
  Speaker 1: to build an infinite spinning cylinder of dust, but it
• 15:30
  Speaker 1: opens up the possibility suggests that maybe there are ways
• 15:33
  Speaker 1: to assemble mass and energy and space so that it
• 15:36
  Speaker 1: bends the fabric of space and time to allow for
• 15:40
  Speaker 1: this kind of motion. Does this actually allow for time travel?
• 15:44
  Speaker 1: Could that really happen? Well, First of all, this isn't
• 15:47
  Speaker 1: like arbitrary time travel. It's not like back to the future.
• 15:50
  Speaker 1: We just dial in when you want to go. This
• 15:52
  Speaker 1: would be a very specific path, and this object would
• 15:56
  Speaker 1: move along this path. But it could only move along
• 15:59
  Speaker 1: this path. It's not like you could go to any
• 16:01
  Speaker 1: specific time or any arbitrary time. You can only move
• 16:04
  Speaker 1: along this worldline through time and space, and it would
• 16:09
  Speaker 1: be a closed loop. So basically you should be on
• 16:11
  Speaker 1: it forever. You can go back and change the past,
• 16:15
  Speaker 1: because that would be off of this closed time like curve.
• 16:18
  Speaker 1: Nor for the curve to exist, it has to reinforce itself,
• 16:21
  Speaker 1: has to be a complete solution, So it doesn't allow
• 16:23
  Speaker 1: for arbitrary time travel. But even still, wouldn't that be
• 16:27
  Speaker 1: weird to have a particle doing a loop in space
• 16:29
  Speaker 1: and time, even if it's stable, even if it doesn't
• 16:32
  Speaker 1: get to go back and kill its own grandparent particle.
• 16:35
  Speaker 1: Is that actually something which could happen on our universe?
• 16:37
  Speaker 1: Doesn't that feel like it violates causality and all sorts
• 16:40
  Speaker 1: of things. Well, theorists are not sure. It seems to
• 16:44
  Speaker 1: work according to general relativity, but people suspect that in
• 16:47
  Speaker 1: practice it probably wouldn't happen, that there's something preventing that.
• 16:52
  Speaker 1: And we know that general relativity is a great theory.
• 16:54
  Speaker 1: We also know it's not a perfect theory. We know
• 16:57
  Speaker 1: that cannot describe the universe as it is because it
• 17:00
  Speaker 1: breaks down it's singularities, like the Big Bang in the
• 17:03
  Speaker 1: center of black holes and all sorts of crazy stuff.
• 17:06
  Speaker 1: And so maybe that this is just an artifact of
• 17:09
  Speaker 1: that theory, a mathematical construction which works most of the
• 17:12
  Speaker 1: time but sometimes gives nonsense answers, And some future theory
• 17:17
  Speaker 1: of space time like quantum gravity, would prevent this from happening.
• 17:20
  Speaker 1: So most theorists, if you ask them, think that there's
• 17:23
  Speaker 1: something out there that would block this from really existing.
• 17:26
  Speaker 1: But to date we do not know, and our best
• 17:29
  Speaker 1: theory about how the universe works. General relativity, which determines
• 17:33
  Speaker 1: how space and time bend in the presence of mass,
• 17:36
  Speaker 1: does not prohibit closed timelike curves. So the jury is
• 17:40
  Speaker 1: still out. So thanks for that awesome question, Autumn. I've
• 17:43
  Speaker 1: been looking forward to digging into time travel and closed
• 17:46
  Speaker 1: timelike curves. Thanks very much for sending that in. I
• 17:49
  Speaker 1: want to get to some more questions, but first let's
• 17:52
  Speaker 1: take a quick break. All right, we're back and we're
• 18:09
  Speaker 1: answering questions from listeners. We've talked about time travel and
• 18:13
  Speaker 1: now we're gonna dig into something even more awesome and futuristic.
• 18:17
  Speaker 1: So here's a great question about force fields. H R.
• 18:20
  Speaker 1: Daniel And if a science fiction inspired question, our force
• 18:24
  Speaker 1: fields possible? Like the ones in Star Trek, everything comes
• 18:28
  Speaker 1: down to particles and arrangement of them in gifin that,
• 18:31
  Speaker 1: for example, of brick walls, just a certain arrangement of particles.
• 18:34
  Speaker 1: Could we mimic that in the air? Okay? I love
• 18:37
  Speaker 1: this question, and mostly because I love the role of
• 18:41
  Speaker 1: science fiction in pushing forward science and inspiring our curiosity.
• 18:45
  Speaker 1: You know, science fiction authors are like the theorists. Of theorists,
• 18:48
  Speaker 1: they think about new crazy things we might be able
• 18:51
  Speaker 1: to do, or ways the universe might work, and they're
• 18:54
  Speaker 1: not limited by mathematics or practicality or anything. And sometimes
• 18:58
  Speaker 1: you read something that they write and you go, I
• 19:00
  Speaker 1: wonder if that is possible or maybe we could actually
• 19:03
  Speaker 1: do that. And so thank you science fiction authors for
• 19:06
  Speaker 1: injecting crazy ideas into the minds of everybody out there
• 19:10
  Speaker 1: and being on the vanguard of creative thinking. So this
• 19:13
  Speaker 1: question is about force fields. Could we build force fields?
• 19:17
  Speaker 1: First of all, we have to talk about what we
• 19:19
  Speaker 1: mean by a force field. And if I was going
• 19:21
  Speaker 1: to commission a force field for my spaceship, for example,
• 19:24
  Speaker 1: because I was about to go into intergalactic war or whatever,
• 19:28
  Speaker 1: here's what I would want. I would want it to
• 19:30
  Speaker 1: be invisible, or at least mostly invisible, because I want
• 19:33
  Speaker 1: to be able to see through it. If I have
• 19:35
  Speaker 1: a spaceship, for example, and a force field around it,
• 19:38
  Speaker 1: I don't want turning on the force field to mean
• 19:40
  Speaker 1: that I can't see anything outside in the universe. Then
• 19:43
  Speaker 1: I'd be a huge strategic disadvantage. So it should be
• 19:47
  Speaker 1: invisible or at least translucent, And then it should block weapons, right,
• 19:51
  Speaker 1: it should be able to absorb radiation weapons like lasers,
• 19:55
  Speaker 1: and it should be able to stop not our weapons
• 19:57
  Speaker 1: like kinetic energy weapons, you know, bullets or other kind
• 19:59
  Speaker 1: of momentum driven weapons. So that's what I'd like, and
• 20:03
  Speaker 1: you know, as a bonus and be cool if you could,
• 20:05
  Speaker 1: for example, be used to hold prisoners. Right, you could
• 20:08
  Speaker 1: like trap somebody who you've captured and put them in
• 20:11
  Speaker 1: the hold view ship and use a force field so
• 20:13
  Speaker 1: you didn't have to build cells and easily configure it
• 20:15
  Speaker 1: and all this kind of stuff. So that's my wish
• 20:17
  Speaker 1: list for a force field. It should be invisible, you
• 20:20
  Speaker 1: should be able to block radiation weapons, and you should
• 20:22
  Speaker 1: be able to block matter weapons, and if possible, you
• 20:25
  Speaker 1: should also be able to touch it without actually being damaged.
• 20:28
  Speaker 1: And that's a long list of requirements. So let's talk
• 20:31
  Speaker 1: about what is actually possible and what might be possible
• 20:35
  Speaker 1: in terms of force fields. So I did a little
• 20:37
  Speaker 1: bit of research in this, and there are people out
• 20:39
  Speaker 1: there actually doing research on force fields. Some of the
• 20:43
  Speaker 1: things don't really seem like the kind of force fields
• 20:45
  Speaker 1: we're talking about. For example, there's a company out there
• 20:48
  Speaker 1: building electric armor. The idea here is to turn the
• 20:51
  Speaker 1: skin of your spaceship or your tank or whatever into
• 20:55
  Speaker 1: something which responds to a bullet. So if somebody shoots
• 20:58
  Speaker 1: a bullet at you, it's not just an in your
• 21:00
  Speaker 1: wall of matter which absorbs that energy and maybe gets destroyed,
• 21:04
  Speaker 1: but it responds to it. So the way they do
• 21:06
  Speaker 1: this is by making two layers of armor and having
• 21:09
  Speaker 1: a huge electrical gap between them, and when something impacts
• 21:13
  Speaker 1: on that armor, it basically closes that gap and results
• 21:17
  Speaker 1: in a huge electric discharge which pushes back on the bullet.
• 21:20
  Speaker 1: It's sort of reactive armor which responds when you're hit
• 21:24
  Speaker 1: with a force backwards. So that's pretty cool. But it's
• 21:27
  Speaker 1: not really a force field. I mean, it's not invisible.
• 21:29
  Speaker 1: You need to build it. You couldn't like turn it
• 21:31
  Speaker 1: on or off, and only works on matter weapons, doesn't
• 21:34
  Speaker 1: stop lasers, for example. But you know, it's something that
• 21:37
  Speaker 1: people are actually doing, and so it's something you might
• 21:40
  Speaker 1: actually see out there in the world soon. But let's
• 21:43
  Speaker 1: talk about what might be possible. You know, when I
• 21:45
  Speaker 1: think about a force field, first, I think about the
• 21:48
  Speaker 1: Earth's force fields, because the Earth actually does have a
• 21:52
  Speaker 1: force field. We have a huge magnetic field that protects
• 21:55
  Speaker 1: the Earth's from particles. The big swirling masses of melted
• 21:59
  Speaker 1: rock and metal in the core of the Earth are
• 22:01
  Speaker 1: providing an enormous magnetic engine, which creates a huge magnetic
• 22:05
  Speaker 1: field with sort of vertical field lines that go from
• 22:07
  Speaker 1: the north to the south or the south to the north.
• 22:10
  Speaker 1: And what this does is when charged particles hit a
• 22:12
  Speaker 1: magnetic field, they get curved, right. This is the Lorenz
• 22:15
  Speaker 1: law in physics. And so an electron, for example, generated
• 22:19
  Speaker 1: in the Sun and given a huge amount of energy
• 22:21
  Speaker 1: and shot towards the Earth, which might otherwise penetrate through
• 22:24
  Speaker 1: the atmosphere and give you cancer instead is bent around
• 22:28
  Speaker 1: these magnetic field lines and funneled up to the north
• 22:31
  Speaker 1: pole or down to the south pole. So that's cool
• 22:34
  Speaker 1: because it's real and it exists. It doesn't really satisfy
• 22:38
  Speaker 1: all of our requirements. I mean, it is invisible and
• 22:40
  Speaker 1: it can deflect matter, but with a couple of big caveats, like,
• 22:44
  Speaker 1: it only works on charged particles, right, It works on electrons,
• 22:48
  Speaker 1: works on protons. It does not work on neutral particles
• 22:50
  Speaker 1: because neutral particles don't feel those magnetic fields. It depends
• 22:54
  Speaker 1: on the charge of the particle. Remember that electricity and
• 22:57
  Speaker 1: magnetism are very tightly woven to get that. They're actually
• 23:00
  Speaker 1: just two sides of the same coin. So these magnetic
• 23:03
  Speaker 1: fields only deflect charge particles. Plus they don't really deflect it,
• 23:07
  Speaker 1: they just sort of focus it on the North Pole
• 23:10
  Speaker 1: and the South Pole. People think, wow, aurora boreality is
• 23:13
  Speaker 1: really cool. It's cool, but it's radiation. So if you
• 23:16
  Speaker 1: live near the North Pole or the South Pole, you
• 23:18
  Speaker 1: actually get more cosmic radiation than anywhere else on Earth
• 23:22
  Speaker 1: because the magnetic field sort of funnels it up there
• 23:24
  Speaker 1: and funnels it down to the South Pole. So it's
• 23:27
  Speaker 1: protecting the rest of the Earth, but at the expense
• 23:29
  Speaker 1: of the North and the Southern caps, so not even
• 23:32
  Speaker 1: really deflecting those charged particles. And then of course it
• 23:35
  Speaker 1: doesn't work on radiation. A magnetic field will not stop
• 23:39
  Speaker 1: a laser beam. A laser beam is made of photons,
• 23:41
  Speaker 1: and photons don't feel magnetic fields, which you know, is
• 23:44
  Speaker 1: kind of weird because photons are partially magnetic fields. They
• 23:48
  Speaker 1: are oscillating electro magnetic waves, right, the electrical component oscillating
• 23:53
  Speaker 1: to the magnetic component and then back. But photons are neutral,
• 23:56
  Speaker 1: they have no electric charge, and so Again, they are
• 23:59
  Speaker 1: not selected by magnetic fields. So a magnetic field kind
• 24:03
  Speaker 1: of like a force field, but not really and also
• 24:05
  Speaker 1: kind of impractical. If you wanted to have a really
• 24:08
  Speaker 1: powerful magnetic force field, you need to be able to
• 24:10
  Speaker 1: generate that inside your spaceship, and you don't really want
• 24:13
  Speaker 1: to have enormous, massive currents of iron and nickel slashing
• 24:18
  Speaker 1: around in the inside of your spaceship to generate this
• 24:20
  Speaker 1: magnetic field. All right, So what else could we do? Well?
• 24:24
  Speaker 1: The third possibility is a plasma shield. Plasma is another
• 24:28
  Speaker 1: state of matter. Basically, you just take gas and you
• 24:31
  Speaker 1: make it even hotter, and then the electrons have so
• 24:34
  Speaker 1: much energy that they whiz off, they leave their protons,
• 24:37
  Speaker 1: and now they're free. So it's ionized gas. You take
• 24:40
  Speaker 1: all the atoms and gas and you break apart the
• 24:43
  Speaker 1: electrons and the nuclei, and that's what a plasma is.
• 24:46
  Speaker 1: It's nothing special or fancy or science fiction. It's just
• 24:49
  Speaker 1: gas that's been heated up so much that the electrons
• 24:51
  Speaker 1: now run free. But it is super duper hot and
• 24:55
  Speaker 1: it's electrically charged, and that means it has the capability
• 24:58
  Speaker 1: to basically vaporize anything. I mean, imagine basically a slice
• 25:02
  Speaker 1: of the Sun. The Sun is plasma, it's super duper hot,
• 25:06
  Speaker 1: and it's ionized. So imagine, for example, having a shield
• 25:09
  Speaker 1: around your spaceship that was a slice of the Sun.
• 25:13
  Speaker 1: You threw anything in it, boom, it would melt. Also,
• 25:16
  Speaker 1: it's opaque. Two lasers, right, A laser can't penetrate the
• 25:20
  Speaker 1: Sun because it's filled with charged particles which would interact
• 25:24
  Speaker 1: with the light in the laser, unless, of course, you
• 25:26
  Speaker 1: tune the laser to be a specific frequency that the
• 25:29
  Speaker 1: plasma didn't absorb. But these excited particles, these free particles,
• 25:33
  Speaker 1: are not limited to absorbing only very specific frequencies. It
• 25:36
  Speaker 1: would be very difficult to get your laser beam through
• 25:39
  Speaker 1: a slice of the Sun through a plasma shield. So
• 25:42
  Speaker 1: that's pretty cool. And actually we have a little bit
• 25:44
  Speaker 1: of a plasma shield already on Earth. The part of
• 25:47
  Speaker 1: the atmosphere we call the ionosphere is basically plasmas filled
• 25:51
  Speaker 1: with ions, and it blocks a lot of radiation from
• 25:55
  Speaker 1: the Sun, neutral radiation, photons, etcetera. And our ionosphere is
• 26:00
  Speaker 1: not very dense but mostly blocks very long wavelength radiation.
• 26:03
  Speaker 1: But if you made a denser plasma, more like a
• 26:06
  Speaker 1: slice of the Sun, then you could block shorter wavelength.
• 26:09
  Speaker 1: So this is the kind of thing you could actually build. Now,
• 26:12
  Speaker 1: how do you make a plasma shield? How is that possible?
• 26:16
  Speaker 1: Can you actually do that? It would be pretty tricky.
• 26:19
  Speaker 1: I mean you need to have basically a shell of gas,
• 26:22
  Speaker 1: and then you need to have that gas get excited
• 26:23
  Speaker 1: to get very very hot. You need to dump a
• 26:26
  Speaker 1: huge amount of energy into it. So you can imagine,
• 26:28
  Speaker 1: for example, puffing out a shell of gas and then
• 26:31
  Speaker 1: zapping it with a bunch of lasers to turn it
• 26:33
  Speaker 1: into a plasma shield. Like essentially deposit so much energy
• 26:37
  Speaker 1: in this shield around you that anything else that comes
• 26:40
  Speaker 1: into it we get absorbed or interacted with or diffused.
• 26:43
  Speaker 1: This is not something that's very easy to do, not
• 26:45
  Speaker 1: something we have the technology to do at all already.
• 26:48
  Speaker 1: It's difficult for us to make and control plasmas. This
• 26:52
  Speaker 1: essentially is the task of fusion. We are trying to
• 26:55
  Speaker 1: replicate what's happening on the Sun in laboratories on Earth,
• 26:58
  Speaker 1: not just so we can build fourth fields, but so
• 27:01
  Speaker 1: that we can generate essentially limitless energy through nuclear fusion,
• 27:05
  Speaker 1: the same process that happens in the center of the Sun,
• 27:08
  Speaker 1: and it's tricky. People have been working on it for decades.
• 27:11
  Speaker 1: They're trying to make a donut of plasma, and they're
• 27:14
  Speaker 1: containing it with magnetic fields. Because the stuff is so
• 27:17
  Speaker 1: volatile it would vaporize any container you put it in.
• 27:20
  Speaker 1: It's so hot and nasty and interactive, so they use
• 27:23
  Speaker 1: a magnetic bottle to contain this plasma. They have basically
• 27:27
  Speaker 1: a donut of the sun, and it's hard to get
• 27:29
  Speaker 1: it to go, it's hard to keep it straight. This
• 27:32
  Speaker 1: is a big engineering challenge, and there's a project going
• 27:34
  Speaker 1: on right now called Eater, which is the biggest and
• 27:37
  Speaker 1: very promising application of this, but it costs billions of
• 27:40
  Speaker 1: dollars and it's not simple to set up. So this
• 27:42
  Speaker 1: would be a very difficult engineering challenge, and you'd have
• 27:45
  Speaker 1: to somehow create this shield around your spaceship, get it
• 27:47
  Speaker 1: zapped up to turn it into a plasma, and then
• 27:50
  Speaker 1: keep it in line with very strong magnets. So possibly
• 27:54
  Speaker 1: you could do that potentially sometime in the future. It
• 27:57
  Speaker 1: might be possible, but it sort of violates one of
• 27:59
  Speaker 1: the first principles we asked for for force field, which
• 28:02
  Speaker 1: is that it's invisible if you surrounded yourself with sort
• 28:05
  Speaker 1: of a sheet of the Sun in a sphere around
• 28:08
  Speaker 1: your ship. Then you wouldn't be able to see anything
• 28:10
  Speaker 1: outside that sphere, and you'd be stuck inside basically a
• 28:14
  Speaker 1: little slice of the sun, which I guess would get
• 28:16
  Speaker 1: pretty hot. So that's sort of the best idea that's
• 28:19
  Speaker 1: out there that I'm aware of to build an actual
• 28:22
  Speaker 1: force field. But it has a lot of engineering challenges
• 28:24
  Speaker 1: ahead of it, and even if we could solve all
• 28:27
  Speaker 1: of those, it doesn't actually satisfy all the requirements we have.
• 28:31
  Speaker 1: So fun question. Maybe somebody in the future will come
• 28:34
  Speaker 1: up with a new way to think about how to
• 28:36
  Speaker 1: actually build a force field. And I shouldn't spy anybody
• 28:39
  Speaker 1: from imagining and from wondering and from being creative. So
• 28:42
  Speaker 1: keep using force fields in the science fiction that you write,
• 28:45
  Speaker 1: and keep an eye out in science fiction for other
• 28:47
  Speaker 1: cool ideas that we might actually turn one day into reality.
• 28:52
  Speaker 1: All right, I want to get to one more question,
• 28:54
  Speaker 1: but first let's take another break. All Right, we are back,
• 29:10
  Speaker 1: and we're having a lot of fun talking about the
• 29:12
  Speaker 1: future and time travel and force fields and future technologies.
• 29:16
  Speaker 1: And now I want to take a trip even deeper
• 29:19
  Speaker 1: into the future, wondering how long humans can survive on Earth, Pie,
• 29:23
  Speaker 1: Daniel and Joey. My name is Gavin and I live
• 29:26
  Speaker 1: in South Wales in the United Kingdom. In the last
• 29:29
  Speaker 1: podcast What's Inside the Earth, You've got me thinking. You
• 29:33
  Speaker 1: told us that the big lump of moon sized core
• 29:36
  Speaker 1: inside the Earth is getting bigger by one millimeter every year,
• 29:40
  Speaker 1: and that at some point in the future the core
• 29:42
  Speaker 1: will stop turning on the Earth will load its magnetic
• 29:45
  Speaker 1: force like we think happened to Mars. My question is, well,
• 29:51
  Speaker 1: this happened before I was set and goes supernova. All right,
• 29:54
  Speaker 1: Thank you very much for that question, and also on
• 29:57
  Speaker 1: behalf of all of humanity, thank you so much for
• 30:00
  Speaker 1: thinking ahead, for worrying because we don't have time to
• 30:03
  Speaker 1: about the deep future, and starting to make plans today
• 30:06
  Speaker 1: for what we might have to do to prepare for it.
• 30:09
  Speaker 1: So he's wondering which of these two calamities will we
• 30:13
  Speaker 1: have to deal with first, the Sun exploding and fiddling
• 30:16
  Speaker 1: out or the earth magnetic field dying, And the two
• 30:19
  Speaker 1: are related, of course, because the earth magnetic field is
• 30:23
  Speaker 1: important for protecting us from the Sun's radiation, so if
• 30:27
  Speaker 1: it disappears then we will be fried. But hey, if
• 30:30
  Speaker 1: it's gonna last longer than the Sun, then we don't
• 30:32
  Speaker 1: need to worry about it. So which one will kill
• 30:35
  Speaker 1: us first is basically the name of the game in
• 30:37
  Speaker 1: this question. So first let's remind ourselves what the timeline
• 30:41
  Speaker 1: is for our sun. How long is this thing? And
• 30:43
  Speaker 1: to keep burning and keeping us toasty and keeping us
• 30:46
  Speaker 1: keeping on. So our son is currently about five billion
• 30:50
  Speaker 1: years old. It's about the age of the Solar system,
• 30:53
  Speaker 1: because it basically is the Solar system. Remember that a
• 30:56
  Speaker 1: coalesced together from a huge cloud of gas and dust
• 31:00
  Speaker 1: and leftovers from population three in population two stars had
• 31:04
  Speaker 1: gathered together in some gravitational event, slowly slurping together, And
• 31:09
  Speaker 1: that most of the stuff in the Solar system is
• 31:12
  Speaker 1: in the Sun. About of everything that's in the Solar
• 31:15
  Speaker 1: system is the Sun, So we're just like a little
• 31:18
  Speaker 1: detail on top of the Sun. Now, that happened about
• 31:21
  Speaker 1: four and a half to five billion years ago, and
• 31:25
  Speaker 1: since then, what's the Sun been doing? Well, it's been
• 31:28
  Speaker 1: burning hydrogen. Gravity gathers together all this material, mostly hydrogen,
• 31:33
  Speaker 1: but also some helium left over from burning from previous generations,
• 31:37
  Speaker 1: and a few other heavier elements, but still overwhelmingly hydrogen
• 31:41
  Speaker 1: and that's good because that's the fuel for the Sun.
• 31:44
  Speaker 1: Gravity squeezes together this hydrogen, and when it gets it
• 31:47
  Speaker 1: close enough, then it confused. Remember that hydrogen is essentially
• 31:51
  Speaker 1: just a proton with an electron around it, but when
• 31:53
  Speaker 1: things get hot, it's basically just a proton. And to
• 31:56
  Speaker 1: make fusion happen, you've got to squeeze to these protons together.
• 32:00
  Speaker 1: But protons are both positively charged and so they resist.
• 32:03
  Speaker 1: And until you get them closed enough together, when the
• 32:06
  Speaker 1: strong force can take over and do nuclear fusion and
• 32:09
  Speaker 1: release a bunch of energy, they will resist. And that's
• 32:11
  Speaker 1: why fusion is hard to make happen. You need really
• 32:14
  Speaker 1: high temperatures and pressures. That's why it's difficult for them
• 32:18
  Speaker 1: to engineer it here on Earth. But anyway, it happens
• 32:20
  Speaker 1: in the Sun, and it's been happening now for about
• 32:23
  Speaker 1: five billion years. So what's going to keep the Sun
• 32:26
  Speaker 1: from burning on forever? Well, eventually it's going to run
• 32:29
  Speaker 1: out of fuel. It's basically a huge hydrogen thermonuclear device.
• 32:34
  Speaker 1: And what happens when it burns hydrogen is that it
• 32:36
  Speaker 1: creates ash. That ash is helium, and it starts at
• 32:39
  Speaker 1: the core because that's where the fusion starts. That's the hottest,
• 32:42
  Speaker 1: densest part. So hydrogen first burns out at the core,
• 32:46
  Speaker 1: and you get this helium core now surrounded by hydrogen,
• 32:50
  Speaker 1: and the fusion is now happening in the sort of
• 32:51
  Speaker 1: outer layers surrounding the core. This pushes out on the Sun,
• 32:55
  Speaker 1: making it bigger and bigger. It fluffs it out, larger
• 32:58
  Speaker 1: and larger, and actually even makes it brighter and brighter.
• 33:02
  Speaker 1: So every year the Sun gets a little bit hotter.
• 33:05
  Speaker 1: In four billion years, for example, the Sun will be
• 33:08
  Speaker 1: about brighter than it is today, and just that is
• 33:12
  Speaker 1: enough to like boil all of the oceans on Earth
• 33:15
  Speaker 1: and turn them into vapor. So right there you can
• 33:17
  Speaker 1: see that in about four billion years, our sun will
• 33:20
  Speaker 1: not make Earth a very cozy place to live in.
• 33:23
  Speaker 1: But as the Sun grows, it's gonna get bigger and bigger.
• 33:26
  Speaker 1: And you might think, well, how much bigger can it get.
• 33:28
  Speaker 1: It's already huge, right, it's already a million times the
• 33:31
  Speaker 1: volume of the Earth. Well it's gonna get bigger by
• 33:33
  Speaker 1: a lot. It's gonna grow by about a factor of
• 33:36
  Speaker 1: two hundred. And that's bad news, because I mean it's
• 33:39
  Speaker 1: gonna get so big that it's radius is going to
• 33:42
  Speaker 1: match the size of Earth's orbit. Right, It's gonna envelop
• 33:45
  Speaker 1: all the inner planets, and the Earth will be right there,
• 33:48
  Speaker 1: right about on the edge of the Sun. What does
• 33:51
  Speaker 1: that mean to be like inside the sun or right
• 33:54
  Speaker 1: just past the edge of the Sun. Well, it's gonna
• 33:57
  Speaker 1: be really hot, and we're gonna be surrounded by these
• 34:00
  Speaker 1: huge sheats of burning hydrogen, which is not going to
• 34:02
  Speaker 1: be a good place to live in. Now, inside the Sun,
• 34:05
  Speaker 1: you now have a helium core which is getting bigger
• 34:08
  Speaker 1: and bigger because as hydrogen burns, it creates more and
• 34:11
  Speaker 1: more helium. Eventually you can even fuse this helium together
• 34:14
  Speaker 1: to make something even heavier carbon. And so this is
• 34:17
  Speaker 1: awesome because it burns hydrogen for millions and millions and
• 34:21
  Speaker 1: billions of years, and then all of a sudden it
• 34:23
  Speaker 1: starts to burn helium. It passes this critical point you
• 34:26
  Speaker 1: can get this helium flash, and the amount of energy
• 34:29
  Speaker 1: generated by the Sun in this moment is actually brighter
• 34:32
  Speaker 1: than all the stars in the galaxy put together, although
• 34:35
  Speaker 1: you don't get to see it because it's absorbed by
• 34:37
  Speaker 1: the inner layers of the Sun. But you know, maybe
• 34:40
  Speaker 1: that's good because otherwise it would fry everything on Earth.
• 34:42
  Speaker 1: So it starts helium fusion, creating carbon, and our sun
• 34:47
  Speaker 1: is not heavy enough. It's not massive enough to then
• 34:49
  Speaker 1: take the next step and fuse carbon into heavier elements.
• 34:52
  Speaker 1: You could eventually make oxygen and neon and silicon and
• 34:55
  Speaker 1: all sorts of crazy stuff if you had a bigger star.
• 34:58
  Speaker 1: Our star is not big enough to do that. So
• 35:01
  Speaker 1: what's gonna happen is it's going to accumulate helium, which
• 35:03
  Speaker 1: will burn into carbon, But then it's sort of stuck there.
• 35:06
  Speaker 1: The carbon is inert and it's like having a lot
• 35:09
  Speaker 1: of ash in your fire. It makes it harder for
• 35:12
  Speaker 1: things to burn, and so the sun will just sort
• 35:14
  Speaker 1: of decrease in brightness from there, basically fizzling out and
• 35:17
  Speaker 1: turning into a white dwarf. A white dwarf is just
• 35:21
  Speaker 1: a hot blob of carbon. It's not fusing anymore, it's
• 35:24
  Speaker 1: not producing any more energy, but it's still really really hot,
• 35:28
  Speaker 1: right it glows. White dwarfs are called white because they
• 35:31
  Speaker 1: do give off light again, not because they're actually fusing
• 35:35
  Speaker 1: they are creating new energy. They're just glowing the same
• 35:37
  Speaker 1: way that anything that's hot glows. It's a white hot
• 35:41
  Speaker 1: lump of carbon in the universe, and so it glows
• 35:43
  Speaker 1: white the way like a really hot piece of metal
• 35:46
  Speaker 1: that you stick into a blacksmith's furnace will also glow
• 35:50
  Speaker 1: white hot, and eventually it will cool. And scientists think
• 35:53
  Speaker 1: that white dwarfs, if given enough time, will eventually radiate
• 35:57
  Speaker 1: off all of their energy and turn into something else,
• 36:00
  Speaker 1: something weird, something called a cold black dwarf. But that
• 36:04
  Speaker 1: will take trillions of years. So let's review the timeline.
• 36:08
  Speaker 1: We're about five billion years into the life cycle of
• 36:10
  Speaker 1: the Sun. It will keep burning for about five billion
• 36:14
  Speaker 1: more years, after which it will envelop the Earth, will
• 36:17
  Speaker 1: have the helium flash, and it will convert into a
• 36:19
  Speaker 1: white dwarf, which won't give off enough heat to keep
• 36:22
  Speaker 1: the Earth warm. But the Earth will have already been
• 36:24
  Speaker 1: fried at that point, and then eventually the white dwarf,
• 36:27
  Speaker 1: in trillions of years, will cool off. So timeline for
• 36:30
  Speaker 1: the Sun to fry us is a few billion years.
• 36:33
  Speaker 1: Now let's turn to the other side of the question,
• 36:36
  Speaker 1: how long will we have a magnetic field for? To
• 36:38
  Speaker 1: answer this question, we need to think about what causes
• 36:41
  Speaker 1: the magnetic field and why that might come to an end.
• 36:44
  Speaker 1: So as we talked about a few minutes ago, the
• 36:46
  Speaker 1: magnetic field we think comes from internal flows of molten
• 36:50
  Speaker 1: rock and metal. And again it's good idea to sort
• 36:52
  Speaker 1: of turn back to the clock and remember how the
• 36:55
  Speaker 1: Earth was formed and why it is the way it is.
• 36:57
  Speaker 1: We think the Earth came together basically a bunch of
• 37:00
  Speaker 1: bits of rock which gathered together into larger bits of rock,
• 37:03
  Speaker 1: into larger bits of rock. So the early Earth was
• 37:06
  Speaker 1: just a collection of rock basically squeezed together, and it
• 37:09
  Speaker 1: wasn't actually melted in the middle yet. Gravity then took
• 37:12
  Speaker 1: over and squeezed it further and further. That plus radioactive
• 37:16
  Speaker 1: decay from certain heavy metals that were embedded in the rock,
• 37:19
  Speaker 1: helps melt the center of the Earth. This might have
• 37:22
  Speaker 1: taken a few hundred million years to melt the center
• 37:25
  Speaker 1: of the Earth to make it molten rather than just
• 37:28
  Speaker 1: hot rock. And this was crucial because it let all
• 37:30
  Speaker 1: the heavy elements, the iron, the nickel, sort of melt down. Right.
• 37:35
  Speaker 1: Things get hot, they get molten, they get liquid. Now
• 37:38
  Speaker 1: you have a fluid instead of rocks, so it's easier
• 37:40
  Speaker 1: for things to sort of like slide around and rearrange themselves.
• 37:43
  Speaker 1: So the heavier elements sink to the core, and now
• 37:46
  Speaker 1: you've get the structure that we have today, which is
• 37:48
  Speaker 1: a solid inner core, very very dense, surrounded by that
• 37:52
  Speaker 1: liquid outer core. And then on top of that is
• 37:55
  Speaker 1: the mantle, which isn't exactly liquid, but it is rock
• 37:58
  Speaker 1: that's sort of flowing. And then on top of that
• 38:00
  Speaker 1: is the crust, the things we actually live on. And
• 38:03
  Speaker 1: we think that it's this molten motion inside the earth.
• 38:06
  Speaker 1: Essentially this liquid outer core that's generating the magnetic field
• 38:10
  Speaker 1: that it's spinning, that there's electric currents in there, and
• 38:13
  Speaker 1: that motion of electric charges creates magnetic fields. Because remember
• 38:17
  Speaker 1: there's a very tight connection between electricity and magnetism. There
• 38:20
  Speaker 1: really are just one thing, electro magnetism, which is why
• 38:24
  Speaker 1: moving particles can generate magnetic fields and why magnetic fields
• 38:28
  Speaker 1: can bend the path of charged particles. So what happens
• 38:31
  Speaker 1: is this stuff is swirling around. It's basically a current,
• 38:34
  Speaker 1: and that creates a magnetic field, and the magnetic field
• 38:37
  Speaker 1: enhances the current. Right, the magnetic field pushes these particles
• 38:41
  Speaker 1: in a circle, and then moving in a circle makes
• 38:43
  Speaker 1: a bigger magnetic field. This is called a dynamo effect. Basically,
• 38:47
  Speaker 1: builds on itself. It makes a stronger and stronger magnetic field,
• 38:50
  Speaker 1: but it relies on the flowing of this liquid molten
• 38:54
  Speaker 1: rock and metal in the center of the Earth outside
• 38:57
  Speaker 1: the inner core. You have to have the ability for
• 38:59
  Speaker 1: this thing to slash around. You need the motion in
• 39:02
  Speaker 1: order to have a magnetic field. And as the question mentioned,
• 39:06
  Speaker 1: this inner core is growing. The Earth is cooling. Basically,
• 39:09
  Speaker 1: it's freezing very slowly, and this core is growing by
• 39:13
  Speaker 1: one millimeter per year, and that's just because things cool, right,
• 39:17
  Speaker 1: We are giving off heat into space the same way
• 39:19
  Speaker 1: that a white dwarf will eventually radiate out all of
• 39:22
  Speaker 1: its energy into space and become a cold black dwarf.
• 39:25
  Speaker 1: Entropy tells us that he should spread out. So you
• 39:28
  Speaker 1: have an isolated hot blob of something in cold space.
• 39:31
  Speaker 1: Eventually it will radiate out its energy. So that's what's
• 39:34
  Speaker 1: happening to Earth. And the inner core is growing, and
• 39:37
  Speaker 1: eventually it will grow and it will cool down the Earth.
• 39:41
  Speaker 1: So how long will this take? Will it be faster
• 39:43
  Speaker 1: than the Sun enveloping the Earth and frying us, or
• 39:46
  Speaker 1: will it be slower. It's difficult to predict these things
• 39:49
  Speaker 1: because it requires projecting out pretty far in time, and
• 39:52
  Speaker 1: our understanding of how these things work inside the Earth
• 39:55
  Speaker 1: is still a little speculative, all right. We've never drilled
• 39:58
  Speaker 1: down to the Earth. A lot of this stuff is
• 40:00
  Speaker 1: reconstructed from seismographs, from basically bouncing waves off the inside
• 40:05
  Speaker 1: of the Earth and understanding how those waves are reflected
• 40:08
  Speaker 1: as they hit various layers inside the Earth. So there's
• 40:11
  Speaker 1: still a lot of guesswork involved. But the best estimate
• 40:14
  Speaker 1: I found is that it will take about ninety billion
• 40:17
  Speaker 1: years for the Earth to lose this magnetic field, essentially
• 40:20
  Speaker 1: for the Earth to freeze internally and to stop having
• 40:23
  Speaker 1: the flowing liquid rock and metal necessary to have a
• 40:27
  Speaker 1: magnetic field. So that's nine one billion years. That's a
• 40:31
  Speaker 1: lot longer than the Sun's expected lifetime. The Sun, we
• 40:35
  Speaker 1: think will fizzle out in about five billion years, So
• 40:38
  Speaker 1: the Earth, if it survives that, if it doesn't just
• 40:40
  Speaker 1: get like melted and slurped into the Sun, would continue
• 40:43
  Speaker 1: on for a long time for tens of billions of
• 40:47
  Speaker 1: years with a magnetic field spinning and reflecting charged particles happily,
• 40:51
  Speaker 1: even if we're now orbiting a white dwarf. So we
• 40:54
  Speaker 1: think the Sun will expand and it will fry the
• 40:57
  Speaker 1: Earth in a few billion years, after which you'll call
• 41:00
  Speaker 1: laps to a white dwarf, and then the Earth, with
• 41:02
  Speaker 1: its magnetic field, will orbit this white dwarf for billions
• 41:05
  Speaker 1: of years until eventually it cools and solidifies and loses
• 41:09
  Speaker 1: its magnetic field in something like ninety billion years. So
• 41:13
  Speaker 1: that's definitely something to think about, something to plan for,
• 41:16
  Speaker 1: something to wonder about. I think personally, we'd be lucky
• 41:20
  Speaker 1: if we made it a billion years on this Earth,
• 41:22
  Speaker 1: so that we have to worry about things like the
• 41:24
  Speaker 1: Sun getting bigger and frying us. We have more immediate
• 41:27
  Speaker 1: problems that we need to tackle, not force fields, not
• 41:30
  Speaker 1: closed timelike curves, but just sort of taking care of
• 41:33
  Speaker 1: the planet so we can last that long. Anyway, it's
• 41:36
  Speaker 1: fun to think about these things, and fun to understand
• 41:38
  Speaker 1: the physics that goes into making a son or making
• 41:41
  Speaker 1: a magnetic field so that you can understand how long
• 41:44
  Speaker 1: they will last. All right, Thanks everybody for sending in
• 41:47
  Speaker 1: these questions and for letting us ride with you on
• 41:49
  Speaker 1: your curiosity journey, for wondering about the nature of a space,
• 41:53
  Speaker 1: for wondering if it's possible to go backwards in time
• 41:56
  Speaker 1: to build force fields and how long this planet Earth
• 41:59
  Speaker 1: will be around for us to live on. It's a
• 42:02
  Speaker 1: joy to get your emails and enjoyed to think about
• 42:04
  Speaker 1: the ideas that are in your head, so please don't
• 42:07
  Speaker 1: be shy send us your questions. Tune in next time.
• 42:18
  Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
• 42:21
  Speaker 1: the Universe is a production of I Heart Radio. Or
• 42:24
  Speaker 1: more podcast from my heart Radio visit the I heart
• 42:27
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• 42:30
  Speaker 1: favorite shows. Ye