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What are land tides? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, when you're at the beach, are you able
• 0:11
  Speaker 1: to relax and forget about physics for a minute.
• 0:13
  Speaker 2: You know, I love the beach. It's beautiful, but it's
• 0:16
  Speaker 2: actually kind of hard to forget about physics at the beach.
• 0:20
  Speaker 2: There's just so much physics happening right there in front
• 0:22
  Speaker 2: of your eyes. The surf, the tides, the shimmering sunlight.
• 0:26
  Speaker 1: It sounds like physics is burnt into your brain.
• 0:29
  Speaker 2: No, it's just the physics is all around us.
• 0:31
  Speaker 3: You know.
• 0:32
  Speaker 2: The moon is up there in the sky literally squeezing
• 0:35
  Speaker 2: the planet with its gravity.
• 0:36
  Speaker 1: Yeah, it sounds like you need some physics sunblock there
• 0:39
  Speaker 1: for your brain.
• 0:40
  Speaker 2: I think you might have to just extract my whole brain.
• 0:43
  Speaker 1: Feed it to the fish.
• 0:43
  Speaker 2: It's good for something.
• 0:44
  Speaker 1: I hope maybe the fish will get smarter. There'll be fishes.
• 1:03
  Speaker 1: Him form a cartoonist and the author of Oliver's Great
• 1:06
  Speaker 1: Big Universe.
• 1:07
  Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor.
• 1:10
  Speaker 2: You see irvine down here on the coast. But I
• 1:12
  Speaker 2: hope not to end up as fish food eventually.
• 1:15
  Speaker 1: Aren't we all fish food or warm food? Which would
• 1:18
  Speaker 1: you prefer to be eaten by worms? Or fish or
• 1:22
  Speaker 1: aliens aliens, But you'll be you'll be food. You won't
• 1:29
  Speaker 1: really have a preference by them.
• 1:31
  Speaker 2: Yeah, but you know, as long as they send me
• 1:32
  Speaker 2: some secrets to the universe before they fry me up
• 1:34
  Speaker 2: for dinner, we're all cool. Nice.
• 1:36
  Speaker 1: It's all about the legacy and what do you know
• 1:39
  Speaker 1: right before you become dinner.
• 1:41
  Speaker 2: Yes, it's a huge difference to die knowing the answers
• 1:44
  Speaker 2: to the secrets of the universe and not.
• 1:47
  Speaker 1: I wonder, though, if your brain is full of all
• 1:49
  Speaker 1: his knowledge, would you cause the aliens indigestion?
• 1:52
  Speaker 2: No? I think I taste better. That's why they should
• 1:55
  Speaker 2: tell me.
• 1:55
  Speaker 1: Sor you'll be juicier. You'll be juicier with knowledge.
• 1:59
  Speaker 2: I mean, I'll be happier, which probably makes me taste better.
• 2:02
  Speaker 2: I don't know.
• 2:03
  Speaker 1: Maybe happiness tastes bitter to the aliens. Maybe I prefer
• 2:06
  Speaker 1: people who don't know a lot of things.
• 2:07
  Speaker 2: In that case, physics is my survival strategy for when
• 2:10
  Speaker 2: the aliens arrive.
• 2:11
  Speaker 1: Taste like a nerd, so nobody wants to eat you.
• 2:13
  Speaker 2: Don't eat me, I'm dorky.
• 2:15
  Speaker 1: Taste don't eat me. I'm a geek. But anyways, welcome
• 2:18
  Speaker 1: to our podcast Daniel and Jorge Explain the Universe, a
• 2:20
  Speaker 1: production of iHeartRadio.
• 2:22
  Speaker 2: In which we do our best to make you filled
• 2:25
  Speaker 2: with knowledge so that you are less tasty to the aliens,
• 2:28
  Speaker 2: or whichever direction that goes. We think that everything out
• 2:32
  Speaker 2: there in the universe can and should be understood, and
• 2:35
  Speaker 2: that everybody out there on Earth is capable of understanding it.
• 2:39
  Speaker 2: And we want to share with you that joyous moment
• 2:41
  Speaker 2: when the idea is click into your head and you go, Aha,
• 2:44
  Speaker 2: that's how it all works.
• 2:46
  Speaker 1: That's right. We like to serve up the entire universe
• 2:48
  Speaker 1: to you on a plate and fill you up with
• 2:50
  Speaker 1: amazing facts and knowledge about how the universe works, what
• 2:54
  Speaker 1: makes it all tick, and what moves the Earth and
• 2:57
  Speaker 1: the oceans out there around us.
• 3:00
  Speaker 2: Some of the deepest questions in physics have to do
• 3:02
  Speaker 2: with what's happening and the objects really far away at
• 3:05
  Speaker 2: the hearts of neutron stars or black holes. Some of
• 3:08
  Speaker 2: them have to do with particles between our toes and
• 3:11
  Speaker 2: how they wiggle and dance and to and fro to
• 3:13
  Speaker 2: make our reality. Sometimes these questions are connected, and what's
• 3:17
  Speaker 2: happening up there in the cosmos affects things down here
• 3:21
  Speaker 2: on Earth.
• 3:21
  Speaker 1: Yeah, it's right. We are surrounded by invisible forces that
• 3:24
  Speaker 1: move the things around us, that cost the weather, the earthquakes,
• 3:28
  Speaker 1: the magnetic field around us, and also the tides.
• 3:32
  Speaker 2: The deep history of physics is just people trying to
• 3:35
  Speaker 2: understand everything they see. Why does it rain? Why does
• 3:38
  Speaker 2: the sun rise? Why does the water rise and fall?
• 3:42
  Speaker 2: Is it possible to understand everything that's happening to us
• 3:45
  Speaker 2: in terms of some like clockwork mechanistic system. If we
• 3:48
  Speaker 2: make our understanding complex enough, can we predict even the
• 3:52
  Speaker 2: rise and fall of the ocean?
• 3:53
  Speaker 1: And so today on the podcast we'll be tackling the
• 3:55
  Speaker 1: question what are land tides now, Daniel, We're not talking
• 4:05
  Speaker 1: about like the closed laundry detergent, are we like the
• 4:08
  Speaker 1: kind of gets dirt out of your clothes tide pods?
• 4:12
  Speaker 2: I think given the poor history of physics naming things,
• 4:16
  Speaker 2: we should be pretty careful drawing conclusions just from the
• 4:19
  Speaker 2: name of this effect.
• 4:20
  Speaker 1: Oh so it is possible to a laundry episode.
• 4:24
  Speaker 2: This episode might be like pouring detergent on your brain.
• 4:27
  Speaker 1: Yes, we're airing out the dirty laundry of physics here.
• 4:31
  Speaker 2: No, In fact, I think this is a topic which
• 4:33
  Speaker 2: is actually probably pretty well named.
• 4:35
  Speaker 1: Oh yes, sometimes it's well named. Sometimes it's not well named.
• 4:38
  Speaker 2: Sometimes the quality of the naming ebbs and.
• 4:40
  Speaker 1: Flows, that's right, And sometimes we like to serve that
• 4:42
  Speaker 1: wave hopefully get to a place where we understand more
• 4:45
  Speaker 1: about the universe and our whole planet. And so this
• 4:48
  Speaker 1: is I guess something that is happening here on Earth,
• 4:51
  Speaker 1: Daniel right.
• 4:52
  Speaker 2: Land tides are happening here on Earth. They're happening on
• 4:54
  Speaker 2: the Moon, They're happening on every planet we.
• 4:56
  Speaker 1: Know of whoa interesting, even the gas planets.
• 5:00
  Speaker 2: I guess they're probably having gas tides. I think there's
• 5:04
  Speaker 2: medication you can take for that.
• 5:05
  Speaker 1: All right, Well, it's an interesting question, and so, as usually,
• 5:07
  Speaker 1: we were wondering how many people out there had thought
• 5:09
  Speaker 1: about the idea of tides on land.
• 5:12
  Speaker 2: Thanks to everybody who volunteers for this audience participation segment.
• 5:15
  Speaker 2: We'd love to hear your voice on our podcast, so
• 5:19
  Speaker 2: please write to me two questions at Daniel and Jorge
• 5:21
  Speaker 2: dot com if you'd like to play.
• 5:23
  Speaker 1: So think about it for a second. What do you
• 5:25
  Speaker 1: think of when you hear the words land tides? Here's
• 5:28
  Speaker 1: what people had to say.
• 5:29
  Speaker 2: Well, we all know what sea tides are I guess
• 5:34
  Speaker 2: it's probably the same effect, but not pulling water, pulling land.
• 5:40
  Speaker 1: Maybe some land that behaves a little bit like water.
• 5:43
  Speaker 1: I don't know.
• 5:43
  Speaker 2: Maybe there are tides in the Sahara Desert that.
• 5:47
  Speaker 4: Makes me think of the ocean tide. So the water
• 5:50
  Speaker 4: being pulled by the Moon. I know, the Earth is
• 5:53
  Speaker 4: kind of being squished a bit from it's not perfectly round,
• 5:57
  Speaker 4: from the gravitational forces and centrifugal force and things like that.
• 6:01
  Speaker 4: So I'm going to guess that that's part of all
• 6:03
  Speaker 4: that together, Especially gravity due to the Moon, the Sun,
• 6:09
  Speaker 4: other you know, astrological bodies all contribute to the land
• 6:13
  Speaker 4: of moving.
• 6:14
  Speaker 3: I haven't heard of land tides before, but I would
• 6:18
  Speaker 3: imagine that they are similar to ocean tides, where the
• 6:22
  Speaker 3: Moon's gravity affects the surface of the Earth, just on
• 6:27
  Speaker 3: land instead of on the ocean.
• 6:29
  Speaker 2: If I had to guess, I would say the effects
• 6:32
  Speaker 2: of tidal force from the Moon non plate tectonics.
• 6:36
  Speaker 1: Seems a little bit straightforward sounding. Perhaps tides related to
• 6:41
  Speaker 1: the land.
• 6:42
  Speaker 2: Yeah, exactly. The name seems to convey basically.
• 6:44
  Speaker 3: What it is.
• 6:45
  Speaker 1: Sounds like I'm the only one who thought about laundry detergent.
• 6:48
  Speaker 1: Might be because it's time for me to do laundry.
• 6:51
  Speaker 1: The tidy my laundry basket is getting a little high.
• 6:53
  Speaker 2: You have a big stack of pajamas.
• 6:55
  Speaker 1: That's right, my daily uniform.
• 6:59
  Speaker 2: It's growing so long that it has its own gravitational pull,
• 7:02
  Speaker 2: and so it's got some tide inside your house.
• 7:04
  Speaker 3: That's right.
• 7:05
  Speaker 1: It's causing the tide of bananas to evan flow just
• 7:08
  Speaker 1: from the sheer gravity of its size.
• 7:11
  Speaker 2: It might cause some marital tides if you're arguing about
• 7:13
  Speaker 2: who's going to do that laundry.
• 7:14
  Speaker 1: Yeah, yeah, yeah, but then it all tides over, so
• 7:17
  Speaker 1: it's all good. Well, let's talk about tides in general,
• 7:20
  Speaker 1: and we'll get to land tides, but first and maybe
• 7:22
  Speaker 1: let's talk about the regular tides most people are familiar with,
• 7:25
  Speaker 1: which are ocean tides or the tides in the sea.
• 7:29
  Speaker 2: Yeah, because it turns out that land tides and ocean
• 7:31
  Speaker 2: tides are pretty intimately connected. So you've got to understand
• 7:35
  Speaker 2: ocean tides first. Ocean tides come from tidal forces. That's
• 7:40
  Speaker 2: how they get their name. And tidal forces are just
• 7:42
  Speaker 2: an effective gravity and of objects not being point masses,
• 7:46
  Speaker 2: of things actually being like extended spheres, so the gravity varies.
• 7:50
  Speaker 2: I mean that gravity gets weaker or stronger as you
• 7:53
  Speaker 2: get further or closer to something. And so if you're
• 7:56
  Speaker 2: in different places on the Earth, for example, you're going
• 7:58
  Speaker 2: to feel the Sun's gravity or the Mund's gravity with
• 8:01
  Speaker 2: a different strength.
• 8:02
  Speaker 1: Well, let's maybe take a step back here and talk
• 8:04
  Speaker 1: about what tides are. So like, if you're at the beach,
• 8:07
  Speaker 1: the tide just means that the general, the average level
• 8:10
  Speaker 1: of the ocean goes up and down.
• 8:11
  Speaker 2: Yeah, when we talk about tides, we usually mean the
• 8:14
  Speaker 2: ocean tides, and yeah, the ocean goes up and it
• 8:17
  Speaker 2: goes down. Like if you're at the beach, sometimes the
• 8:19
  Speaker 2: water rises up higher than it does other times. And
• 8:22
  Speaker 2: you might notice when you're sitting there on the sand,
• 8:23
  Speaker 2: you take a nap and you wake up, Oops, you're underwater.
• 8:27
  Speaker 2: And that's not because of a rogue wave. It's because
• 8:29
  Speaker 2: the overall level of the ocean has risen.
• 8:32
  Speaker 1: When do you think humans first noticed this? Probably the
• 8:34
  Speaker 1: first time they reached the beach, right.
• 8:36
  Speaker 2: Yeah, I think people have always noticed this. I mean
• 8:39
  Speaker 2: people have been living on the beach in southern California
• 8:41
  Speaker 2: for tens of thousands of years and so pretty sure
• 8:44
  Speaker 2: tides were part of their life.
• 8:45
  Speaker 1: Right, But I imagine they started in the beaches of
• 8:47
  Speaker 1: Africa perhaps.
• 8:49
  Speaker 2: Oh yeah, absolutely, there's tides on every shore around the world.
• 8:52
  Speaker 1: And now does it depend on the size of the
• 8:54
  Speaker 1: body of water, Like is it bigger in some oceans
• 8:57
  Speaker 1: or lakes? Does it happen in a lake.
• 8:59
  Speaker 2: It turns out to be quite complicated the size of
• 9:02
  Speaker 2: the tides. It depends on not just the depth of
• 9:05
  Speaker 2: the ocean and the size of the body of water,
• 9:08
  Speaker 2: but also like the shape of the harbor and the
• 9:11
  Speaker 2: shape of the land nearby. There's all sorts of complicated
• 9:14
  Speaker 2: effects that change how the ocean water goes up and
• 9:17
  Speaker 2: down at a particular point on the shore.
• 9:20
  Speaker 1: All right, Well, let's dig into the physics. You said
• 9:22
  Speaker 1: it's sort of related to the gravity of the moon.
• 9:25
  Speaker 2: The reason the ocean goes up and down is mostly
• 9:27
  Speaker 2: because of the moon, also because of the Sun. The
• 9:30
  Speaker 2: physics that underlies it is what we call tidal forces.
• 9:33
  Speaker 2: If the moon is pulling on you, then it pulls
• 9:35
  Speaker 2: on you harder. If you're on a spot on the
• 9:37
  Speaker 2: Earth it's closer to the Moon than if you're on
• 9:39
  Speaker 2: the other side of the Earth.
• 9:41
  Speaker 1: And that's because that's just how gravity works, right.
• 9:43
  Speaker 2: Yeah, that's how gravity works. The closer you are the
• 9:46
  Speaker 2: heart of the force. So physicists tend to like to
• 9:49
  Speaker 2: think about planets as point particles or Earth is just
• 9:52
  Speaker 2: like a dot that has the mass of the Earth
• 9:54
  Speaker 2: at its center of mass, and we think about the
• 9:56
  Speaker 2: motion of the Earth using fat But in actuality, every
• 10:00
  Speaker 2: place on the Earth feels a different tug from the
• 10:03
  Speaker 2: Moon because they're all at different distances and different angles.
• 10:06
  Speaker 1: Right Like, if you were just out there in space,
• 10:09
  Speaker 1: if you were closer to the Moon, you would feel
• 10:10
  Speaker 1: a stronger pull towards the Moon than if you were
• 10:12
  Speaker 1: farther away from the Moon. And so the same thing
• 10:15
  Speaker 1: happens to all the points around the Earth.
• 10:17
  Speaker 2: The same thing happens to all the points around the Earth.
• 10:19
  Speaker 2: And this isn't just connected to the Moon or to
• 10:21
  Speaker 2: the Sun. It happens for everything that's gravitational. We talk
• 10:25
  Speaker 2: about it in the context of black holes because black
• 10:27
  Speaker 2: holes are extremely strong gravity. If you get too close
• 10:30
  Speaker 2: to them, then the difference between the gravity on your
• 10:33
  Speaker 2: feet and on your head might be strong enough to
• 10:35
  Speaker 2: pull you apart. That's the origin of spaghetification. It's just
• 10:39
  Speaker 2: tidal forces. The fact that you're not a point particle.
• 10:42
  Speaker 2: If you're just a point particle, there'd be one force
• 10:44
  Speaker 2: of gravity on you. But because you're an extended object
• 10:47
  Speaker 2: with different distances from the black hole or from the
• 10:49
  Speaker 2: Moon or from the Sun, you feel different forces of
• 10:52
  Speaker 2: gravity at different points on your body.
• 10:54
  Speaker 1: Interesting. So then where does the word title come in?
• 10:57
  Speaker 2: Oh, the word title comes in because this is base
• 11:00
  Speaker 2: an explanation for the ocean tides. So that's why we
• 11:03
  Speaker 2: call them tidal forces, all.
• 11:04
  Speaker 1: Right, So then how does the moon cause the tides
• 11:07
  Speaker 1: in the ocean?
• 11:08
  Speaker 2: So the way to think about tidal forces is to
• 11:10
  Speaker 2: think about how the force of gravity on you is
• 11:13
  Speaker 2: different than if you were at the center of the Earth.
• 11:16
  Speaker 2: The center of the Earth is sort of like the
• 11:17
  Speaker 2: reference gravity. If you're at the center of the Earth,
• 11:19
  Speaker 2: what would be the gravity of the moon. And then
• 11:21
  Speaker 2: as you move around the surface of the Earth, you
• 11:23
  Speaker 2: can ask how is my gravity different than if I
• 11:25
  Speaker 2: was at the center of the Earth. And so if
• 11:27
  Speaker 2: you're on a point on the Earth that's closer to
• 11:30
  Speaker 2: the Moon than the center, then you're going to feel
• 11:32
  Speaker 2: stronger gravity towards the Moon. If you're on the other
• 11:35
  Speaker 2: side of the Earth. Now you're farther from the Moon,
• 11:38
  Speaker 2: you're going to feel weaker gravity. So the tidal force
• 11:41
  Speaker 2: is the difference. So what that means is that on
• 11:44
  Speaker 2: the closer side of the Earth, there's basically a tidal
• 11:46
  Speaker 2: force towards the Moon, and on the distant side of
• 11:49
  Speaker 2: the Earth is a tidal force away from the moon.
• 11:52
  Speaker 1: Oh why is it away? And I still being pulled
• 11:55
  Speaker 1: towards the moon even if I'm on the far side
• 11:58
  Speaker 1: of the Earth.
• 12:00
  Speaker 2: Are still being pulled towards the moon. The force of
• 12:02
  Speaker 2: gravity is towards the Moon, but it's less than the
• 12:04
  Speaker 2: force of gravity you would feel at the center of
• 12:06
  Speaker 2: the Earth. So relative to the force of the center
• 12:09
  Speaker 2: of the Earth, the tidal force is away from the Moon.
• 12:12
  Speaker 1: I see, you're being pulled less than the center. So
• 12:14
  Speaker 1: in a way, you're being pulled away from the center
• 12:16
  Speaker 1: of the Earth exactly.
• 12:17
  Speaker 2: And that's all we usually talk about, how one part
• 12:20
  Speaker 2: is being pulled towards and one part is effectively being
• 12:22
  Speaker 2: pulled away in a relative sense. But this also sort
• 12:25
  Speaker 2: of sideways tidal forces. If you're at a point along
• 12:29
  Speaker 2: a circle that's between the point that's closest to the
• 12:32
  Speaker 2: Moon and the point that's furthest from the Moon. Then
• 12:34
  Speaker 2: the effective tidal forces are towards the center of the
• 12:37
  Speaker 2: Earth because the Moon is pulling you not just towards
• 12:40
  Speaker 2: the Moon, but also basically towards the center of the Earth.
• 12:43
  Speaker 1: So, for example, like the moon sort of rotates around
• 12:46
  Speaker 1: the Earth sort of along the equator line more or less, right,
• 12:50
  Speaker 1: Like that's the kind of the circle that goes around
• 12:52
  Speaker 1: and A. So you're saying, like the north and south
• 12:54
  Speaker 1: poles of the Earth are being pulled kind of towards
• 12:58
  Speaker 1: the equator basically.
• 13:00
  Speaker 2: Yeah, that's right. And so the overall effect is just
• 13:03
  Speaker 2: try to squeeze the Earth like into a football shape.
• 13:06
  Speaker 2: The closest part gets pulled closer, the furthest part gets
• 13:09
  Speaker 2: pulled less, and the center gets squeezed towards the center
• 13:12
  Speaker 2: of the Earth.
• 13:14
  Speaker 1: All right, So then the effect of the Moon is
• 13:16
  Speaker 1: to squish the Earth. It's not just like pulling at
• 13:18
  Speaker 1: the center of the Earth. It's like kind of pulling
• 13:20
  Speaker 1: out the Earth, but also kind of squishing it or
• 13:23
  Speaker 1: kind of trying to pull into a football shape.
• 13:25
  Speaker 2: Yeah, exactly, And this is all relative to how the
• 13:28
  Speaker 2: Moon would be pulling on the Earth. If it's just
• 13:30
  Speaker 2: like a point particle at the center of mass, because
• 13:33
  Speaker 2: the Earth isn't. The point particle has all these different
• 13:36
  Speaker 2: gravitational forces on it, and the effect is basically to
• 13:39
  Speaker 2: try to squeeze it into a football.
• 13:40
  Speaker 1: And the weird thing is that the Moon is moving
• 13:42
  Speaker 1: relative to the Earth, so it's like it's squeezing in
• 13:44
  Speaker 1: one moment, it's squeezing it in one direction to make
• 13:46
  Speaker 1: it look like football. But then as the Moon rotates,
• 13:49
  Speaker 1: then now all those forces changes, so it's almost like
• 13:52
  Speaker 1: you're massaging the Earth exactly.
• 13:54
  Speaker 2: You're massaging the Earth, and you're running circles around the
• 13:57
  Speaker 2: Earth at the same time, so you're always massaging different spots.
• 14:00
  Speaker 1: Yeah, it's a three sixty massage.
• 14:03
  Speaker 2: And that's the origin of the tidal patterns, right the
• 14:05
  Speaker 2: tides go up and the tides go down. Basically, the
• 14:08
  Speaker 2: water on the surface of the Earth gets pulled into
• 14:11
  Speaker 2: that football shape because water is much more flexible than
• 14:14
  Speaker 2: the earth is, So the water is deeper the conical
• 14:16
  Speaker 2: parts of that football and shallower at the edges of
• 14:20
  Speaker 2: the football.
• 14:21
  Speaker 1: What do you mean, it's more flexible.
• 14:22
  Speaker 2: It's easier to squeeze water than it is to squeeze granite.
• 14:26
  Speaker 1: Or in this case, you're saying it's easier to stretch water.
• 14:29
  Speaker 2: Yeah, exactly, to stretch water.
• 14:31
  Speaker 1: So like the parts of the the equator there are
• 14:32
  Speaker 1: closest to the Moon, the Earth is being squeezed and stretched,
• 14:36
  Speaker 1: but the water on the surface on that side is
• 14:38
  Speaker 1: getting stretched even more, and that's what causes the tides.
• 14:42
  Speaker 2: And that's what causes the tides. Not just the Moon though,
• 14:45
  Speaker 2: right the Sun also plays a role because there's tidal
• 14:47
  Speaker 2: forces from the Sun. The Sun also has gravity on
• 14:51
  Speaker 2: the Earth, and as the Earth moves around the Sun,
• 14:53
  Speaker 2: different parts of the Earth feel gravity differently from the
• 14:56
  Speaker 2: Sun because there are different distances from the Sun.
• 15:00
  Speaker 1: Says maybe as a kid, I thought that maybe I
• 15:02
  Speaker 1: knew that the tides were caused by the Moon, but
• 15:05
  Speaker 1: I thought maybe it was like it was pulling the water.
• 15:07
  Speaker 1: And so it's basically like sucking all the water to
• 15:09
  Speaker 1: one side of the Earth, like it's bringing water from
• 15:12
  Speaker 1: the far side of the Earth to the near side
• 15:13
  Speaker 1: of the Earth facing the Moon.
• 15:15
  Speaker 2: It is doing that, but on the other side, it's
• 15:17
  Speaker 2: also sort of pulling the Earth harder than it's pulling
• 15:20
  Speaker 2: the water, and so it's leaving some of the water behind,
• 15:23
  Speaker 2: so you get deeper water on the spot closest to
• 15:25
  Speaker 2: the Moon and on the other side as well.
• 15:28
  Speaker 1: Whoa wait, wait, wait, but I thought the water was
• 15:31
  Speaker 1: more squishable.
• 15:32
  Speaker 2: Water is more squishable, so it responds more quickly to
• 15:35
  Speaker 2: these tidal forces. So the tidle forces on the spot
• 15:37
  Speaker 2: closest to the Moon are pulling it towards the Moon,
• 15:40
  Speaker 2: making that water deeper. The tidal forces on the spot
• 15:43
  Speaker 2: opposite side are pushing things away from the center of
• 15:47
  Speaker 2: the Earth, and so that's sort of pushing that water
• 15:49
  Speaker 2: up and then around the circumference it's squeezing it. So
• 15:52
  Speaker 2: squeezes that water and pushes it towards the sort of
• 15:55
  Speaker 2: cones of the football.
• 15:56
  Speaker 1: Mmmm. And so like if you look at a tide
• 15:59
  Speaker 1: schedule for a bee, which you're seeing like the dynamics
• 16:02
  Speaker 1: of the Moon and the Sun and the effects they
• 16:04
  Speaker 1: have on the Earth. Yeah, exactly, It's like this dance
• 16:07
  Speaker 1: between all three things is what causes those weird tidal charts.
• 16:10
  Speaker 2: Yeah, the dance between those three things is part of
• 16:12
  Speaker 2: the explanation. The Moon dominates. Of course, the Sun is
• 16:15
  Speaker 2: much more massive and has more gravity, but we're much
• 16:18
  Speaker 2: further from the Sun, and on balance, the Moon's tidal
• 16:21
  Speaker 2: forces are like two times as powerful as the Sun's. Overall,
• 16:25
  Speaker 2: this is a pretty tiny effect relative to Earth's gravity.
• 16:28
  Speaker 2: It's like one part per million or less variation in
• 16:31
  Speaker 2: the Earth's gravity, but it can cause big effects. Like
• 16:34
  Speaker 2: there's places in Canada where there's a sixteen meter difference
• 16:38
  Speaker 2: between the low tide and the high tide.
• 16:40
  Speaker 1: Whoa wait, sixteen meter difference in the height of the water,
• 16:45
  Speaker 1: or like the shoreline in the height of the water.
• 16:47
  Speaker 1: Oh wow, why is it more there than in other places?
• 16:50
  Speaker 2: So there's a bunch of different things going on. Number
• 16:52
  Speaker 2: one is it's not just the simple model of the
• 16:54
  Speaker 2: Earth and the Moon. Also, the Moon is sort of
• 16:57
  Speaker 2: declined relative to the Earth. It's not actually orbiting around
• 17:00
  Speaker 2: the equator, which means that like sometimes it's closer to
• 17:03
  Speaker 2: the northern hemisphere and sometimes it's closer to the southern hemisphere.
• 17:07
  Speaker 2: So you get this cycle they call a fortnightly cycle
• 17:10
  Speaker 2: fortnite meeting every two weeks, because the Moon's orbit is
• 17:13
  Speaker 2: about a month obviously, and so every two weeks you're
• 17:16
  Speaker 2: in one half of the cycle and every two weeks
• 17:18
  Speaker 2: you're in the other half of the cycle. So there's
• 17:20
  Speaker 2: lots of these little effects that are all gravitational that
• 17:23
  Speaker 2: tug on the water differently. And then there's the response
• 17:26
  Speaker 2: of the water. So it depends on like the shape
• 17:28
  Speaker 2: or the harbor and how the deep ocean tides are
• 17:31
  Speaker 2: affected and all sorts of like resonance effects in the
• 17:34
  Speaker 2: water because you're pulling on the water, but it's not
• 17:36
  Speaker 2: responding instantaneously that it's sloshing around, So which is why
• 17:40
  Speaker 2: you get different tides in different places.
• 17:42
  Speaker 1: Right, Like I think in the Caribbean Ocean the tide
• 17:46
  Speaker 1: changes are much less than in the Pacific Ocean, for example.
• 17:49
  Speaker 2: Mm hmm, yeah, exactly. So it depends on the depth
• 17:52
  Speaker 2: of the water, depends on the shape of the shore,
• 17:54
  Speaker 2: it depends on how the water is flowing. It's very complicated,
• 17:58
  Speaker 2: and actually out there in the deep ocean, we don't
• 18:00
  Speaker 2: know very much about the effective tides and the depths
• 18:02
  Speaker 2: of them. We've measured them on the shore because they're
• 18:05
  Speaker 2: very important for boats coming in and boats leaving, but
• 18:08
  Speaker 2: out there in the deep ocean it's much murkier.
• 18:10
  Speaker 1: Well, I wonder if it's a bigger effect, Like the
• 18:12
  Speaker 1: deeper the ocean is, the more it's going to basically
• 18:15
  Speaker 1: get stretched by the moon. So like maybe in the
• 18:17
  Speaker 1: middle of the ocean, the height of the ocean is
• 18:20
  Speaker 1: changing a lot.
• 18:21
  Speaker 2: Yeah, exactly. We just have fewer sensors out there and
• 18:24
  Speaker 2: fewer like immediate reasons to know. We're curious from a
• 18:26
  Speaker 2: sort of like geological perspective, you know, for people who
• 18:30
  Speaker 2: really want to understand the tides, but it's not as
• 18:33
  Speaker 2: important for understanding like when your tunic crawler is going
• 18:36
  Speaker 2: to come back.
• 18:36
  Speaker 1: All right, well, let's dig into what land tides are
• 18:40
  Speaker 1: now and how those affect the shape of the Earth
• 18:43
  Speaker 1: and maybe how these forces can also affect our whole galaxy.
• 18:47
  Speaker 1: So let's dig into that. But first let's take a
• 18:49
  Speaker 1: quick break. All right, we're talking about tides now, Daniel,
• 19:04
  Speaker 1: what's the history of tides and our understanding of them.
• 19:07
  Speaker 2: Yeah, we've known about tides forever, right, as long as
• 19:10
  Speaker 2: we've known about lightning and rain and all sorts of stuff,
• 19:13
  Speaker 2: and people have been wondering for a long time about
• 19:16
  Speaker 2: the cause of it and trying to understand it. And
• 19:18
  Speaker 2: it's obviously connected to the moon, right, the cycles of
• 19:21
  Speaker 2: the moon are connected to the tides, and so as
• 19:24
  Speaker 2: far back as the Greeks, we have records of people
• 19:26
  Speaker 2: speculating that somehow the moon caused it. The Greeks had
• 19:31
  Speaker 2: no understanding of gravity as we do, of course, so
• 19:34
  Speaker 2: they definitely didn't understand tidal forces and couldn't put together
• 19:37
  Speaker 2: like a mechanistic explanation.
• 19:39
  Speaker 1: But somehow they knew is related to the moon.
• 19:41
  Speaker 2: They suspected it was related to the moon, just because
• 19:44
  Speaker 2: it's linked to lunar cycles, right, is it?
• 19:46
  Speaker 1: I don't know, like it the tide goes up and
• 19:49
  Speaker 1: down twice a day, I think for most beaches, at
• 19:52
  Speaker 1: least in California, But I don't see the moon go
• 19:54
  Speaker 1: up and down twice a day.
• 19:56
  Speaker 2: I think if you keep close track of where the
• 19:58
  Speaker 2: Moon and the Sun and the Earth are, and the
• 20:00
  Speaker 2: Greeks definitely did this, and we have also evidence of
• 20:02
  Speaker 2: Islamic astronomers doing this. You notice the connection between where
• 20:06
  Speaker 2: the moon is and where the tides are, right, because
• 20:09
  Speaker 2: remember it's the location of the moon that's dictating. It's
• 20:11
  Speaker 2: where the moon is closest to the Earth is where
• 20:13
  Speaker 2: there are going to be high tides, and then also
• 20:15
  Speaker 2: on the other side of it. So the location of
• 20:17
  Speaker 2: the Moon is definitely connected to the height of the tides.
• 20:20
  Speaker 2: You don't need to know gravity just to see this connection.
• 20:24
  Speaker 1: But is our wonder if there's a delay, like do
• 20:26
  Speaker 1: you see a delay between when the moon is closest
• 20:29
  Speaker 1: to the Earth and when the tides are highest.
• 20:31
  Speaker 2: There's definitely a delay, right, because water doesn't respond instantaneously
• 20:34
  Speaker 2: and there are all these other effects. But people have
• 20:37
  Speaker 2: been debating what the actual mechanism was. Galileo, for example,
• 20:40
  Speaker 2: suggested that it just had to do with the sloshing
• 20:43
  Speaker 2: of water as the Earth moon around the Sun. He
• 20:46
  Speaker 2: thought that if you had an object covered in water
• 20:48
  Speaker 2: and it was orbiting the Sun, that the water was
• 20:50
  Speaker 2: going to slosh around it the way like a bucket
• 20:52
  Speaker 2: would slash as you walk with.
• 20:53
  Speaker 1: It, or whonderver. They thought like maybe there's a like
• 20:56
  Speaker 1: a giant tick in a bath in the ocean, Like
• 20:59
  Speaker 1: did they think maybe, you know, like the archimittees of fact,
• 21:01
  Speaker 1: like if you get an ocean the water rises, Did
• 21:05
  Speaker 1: they think maybe it was related to something.
• 21:07
  Speaker 2: Like that, that'd be a very regular giant. Yeah. The
• 21:09
  Speaker 2: Greeks probably did have some mythology related to the tides.
• 21:12
  Speaker 2: Poseidon probably controlled them. I'm not an expert in that,
• 21:16
  Speaker 2: but the first real explanation for the tides in terms
• 21:18
  Speaker 2: of a mechanism comes of course from Isaac Newton in
• 21:21
  Speaker 2: his groundbreaking where Principia, where he lays out the theory
• 21:24
  Speaker 2: of gravity. He's also at the same time able to
• 21:27
  Speaker 2: explain the tides and why the tides happen twice a
• 21:31
  Speaker 2: day because the water piles up at the spot closest
• 21:33
  Speaker 2: to the moon and the spot furthest.
• 21:35
  Speaker 1: Interesting because the Moon goes around the Earth once a day,
• 21:38
  Speaker 1: or I guess technically the Earth spins once a day.
• 21:41
  Speaker 2: Yeah, the motion of the Moon relative to the Earth
• 21:44
  Speaker 2: is roughly once per day. Yeah, that's what a day
• 21:46
  Speaker 2: is really.
• 21:46
  Speaker 1: And then later, I guess we got fancier with the
• 21:48
  Speaker 1: models of this and we're able to predict more accurately
• 21:51
  Speaker 1: what the tides are going to be.
• 21:53
  Speaker 2: Yeah, exactly. Newton's calculations allow you to predict the forcing,
• 21:56
  Speaker 2: like how much force there is from the Moon on
• 21:59
  Speaker 2: the water, but the actual motion of the water requires
• 22:02
  Speaker 2: you to understand fluid dynamics and ocean depth and take
• 22:05
  Speaker 2: ato account like the Earth's rotation and the shape of
• 22:07
  Speaker 2: the coast, and so Over the last few hundred years
• 22:10
  Speaker 2: people have added all that understanding to a model of
• 22:13
  Speaker 2: the tides, and now we can predict the tides like
• 22:15
  Speaker 2: years in advance at any point on the coast.
• 22:19
  Speaker 1: Wow, just from the position of the moon where we
• 22:21
  Speaker 1: know it's going to be in the future, and the.
• 22:23
  Speaker 2: Sun exactly, and the models of the ocean and the
• 22:25
  Speaker 2: Earth's rotation taking all of this into account.
• 22:28
  Speaker 1: M all right, Well, let's get to the question of
• 22:30
  Speaker 1: the episode, which is what are land tides?
• 22:33
  Speaker 3: Now?
• 22:34
  Speaker 1: Daniel, I don't see the land going up and down
• 22:36
  Speaker 1: at the beach or anywhere, So what does this term mean?
• 22:41
  Speaker 2: So the term means exactly what you think. It means
• 22:43
  Speaker 2: that the Earth's land goes up and down the same
• 22:46
  Speaker 2: way that water in the ocean does. It's just that
• 22:49
  Speaker 2: the Earth doesn't respond the same way the ocean does
• 22:51
  Speaker 2: because the Earth is not made of water.
• 22:54
  Speaker 1: All right, So what do you mean by the land tide?
• 22:56
  Speaker 1: Am I going to see this effect? Or am I
• 22:59
  Speaker 1: just gonna have to think about the idea that maybe
• 23:01
  Speaker 1: I'm further away from the center of the Earth sometimes
• 23:04
  Speaker 1: than other times.
• 23:05
  Speaker 2: It's not something you need to factor into your daily life.
• 23:08
  Speaker 2: It's not really gonna change your drive to work, or
• 23:11
  Speaker 2: even if you work on like a shrimp trawler or
• 23:13
  Speaker 2: any sort of ocean vessel. It's not really gonna affect you,
• 23:15
  Speaker 2: but it is cool, I think to understand that the
• 23:17
  Speaker 2: whole earth is being squeezed. The taidle forces don't just
• 23:20
  Speaker 2: affect the water. The earth is also there feeling them.
• 23:23
  Speaker 2: And the earth is not perfectly rigid. Right, Yes, it's
• 23:27
  Speaker 2: made of rock, which is definitely stiffer than the water,
• 23:30
  Speaker 2: but it's not perfectly rigid, and so it responds.
• 23:33
  Speaker 1: Meaning like you can technically squeeze and stretch rock. Right,
• 23:36
  Speaker 1: It won't stretch or squeeze a lot, but technically it's
• 23:39
  Speaker 1: gonna move a little bit, tiny bit.
• 23:40
  Speaker 2: Yeah, exactly, and it's not even a tiny little bit.
• 23:43
  Speaker 2: I was reading a calculation that says that New York
• 23:46
  Speaker 2: City rises by more than a foot as these land
• 23:49
  Speaker 2: tides progress.
• 23:50
  Speaker 1: Whoa, but relative to what I guess, yeah.
• 23:54
  Speaker 2: Relative to the center of the earth. So it's not
• 23:57
  Speaker 2: something you notice because it's not like one block in
• 23:59
  Speaker 2: Manhattan moves up a foot relative to another block. The
• 24:02
  Speaker 2: whole city moves together as the crust of the earth
• 24:06
  Speaker 2: is flexing.
• 24:08
  Speaker 1: Basically, you're sort of treating the earth like a bouncy ball, right,
• 24:11
  Speaker 1: or like one of those stress balls.
• 24:12
  Speaker 2: Yeah. And part of the history here is really cool
• 24:14
  Speaker 2: because it goes back to when people were trying to
• 24:16
  Speaker 2: figure out what is the Earth made out of? Like
• 24:19
  Speaker 2: is the Earth just a big ball of solid rock
• 24:21
  Speaker 2: or is it totally molten and fluid? Like is the
• 24:24
  Speaker 2: Earth a water balloon or is it a marble or
• 24:28
  Speaker 2: is it a bouncy ball? And so people were trying
• 24:30
  Speaker 2: to figure this out hundreds of years ago, before they
• 24:33
  Speaker 2: could like dig into the earth, or before we had
• 24:35
  Speaker 2: modern seismology that reveals what's going on inside of the
• 24:38
  Speaker 2: Earth by how earthquakes like bounce around on all the
• 24:40
  Speaker 2: internal layers.
• 24:41
  Speaker 1: You mean more like a lava balloon.
• 24:43
  Speaker 2: Yeah, a lava balloon exactly. In the late eighteen hundreds,
• 24:47
  Speaker 2: the prevailing theory of what was inside the Earth was
• 24:50
  Speaker 2: that it was molten. Right, people saw lava, and oh, well,
• 24:53
  Speaker 2: maybe the Earth is just filled with lava, right, maybe
• 24:56
  Speaker 2: it's fluid. So then scientists try to calculate like, all right,
• 24:59
  Speaker 2: well then, and what should be the earth tides? If
• 25:02
  Speaker 2: the Earth is just a balloon filled with lava, then
• 25:05
  Speaker 2: Lord Kelvin actually calculated that we should have huge earth
• 25:09
  Speaker 2: tides because if the Earth is as flexible as the
• 25:12
  Speaker 2: ocean is. Right, if it's just basically an ocean of
• 25:15
  Speaker 2: lava underneath a thin crust, then we should be seeing
• 25:18
  Speaker 2: huge tides as big as we see in the ocean.
• 25:21
  Speaker 1: But would lava be as quishable as water, Isn't it
• 25:25
  Speaker 1: the thicker and more denser.
• 25:26
  Speaker 2: Yeah, it's definitely thicker and denser. So it's not exactly
• 25:29
  Speaker 2: like water. But if you take all that into account,
• 25:32
  Speaker 2: you predict huge earth tides, you predict that the land
• 25:35
  Speaker 2: was should change by meters and meters, and we definitely
• 25:38
  Speaker 2: didn't see that. And so that's one very early sign
• 25:41
  Speaker 2: they had that the earth is more rigid than water internally.
• 25:44
  Speaker 2: It's just like a way to see what's inside the
• 25:46
  Speaker 2: earth without even looking inside.
• 25:49
  Speaker 1: So if the earth was made out of all a
• 25:51
  Speaker 1: lava inside, we would we would basically see New York
• 25:53
  Speaker 1: City rise and fall by a lot more than a
• 25:56
  Speaker 1: food Yeah, exactly would Like would you would you? I
• 26:00
  Speaker 1: guess you would see it as a wave, like New
• 26:02
  Speaker 1: York City would rise a bunch and then go down,
• 26:04
  Speaker 1: and then you know New Jersey or Pennsylvania would then
• 26:09
  Speaker 1: rise and fall, right, that's kind of the idea.
• 26:11
  Speaker 2: Yeah, And you would have much more dramatic like earthquakes,
• 26:13
  Speaker 2: because land tides can cause a lot of pressure on
• 26:16
  Speaker 2: the boundaries between the plates and cause all sorts of earthquakes,
• 26:20
  Speaker 2: So it would make life on Earth much more dramatic.
• 26:23
  Speaker 1: But thankfully we're not a giant love of ball. We're
• 26:27
  Speaker 1: fairly rigid. We're mostly rock up until the core of
• 26:31
  Speaker 1: the earth, right or the inner mantle.
• 26:33
  Speaker 2: Yeah, it's quite dense, but it is actually pretty fluid.
• 26:36
  Speaker 2: But the outer edge is pretty hard and definitely much
• 26:38
  Speaker 2: less fluid than water. So original calculations by Lord Kelvin,
• 26:42
  Speaker 2: the fact that he couldn't see any earth tides himself,
• 26:45
  Speaker 2: basically let him estimate that the internal part of the
• 26:48
  Speaker 2: Earth was more rigid than glass, but less rigid than
• 26:52
  Speaker 2: iron for example, so very very rough. And then around
• 26:56
  Speaker 2: one hundred years ago people started trying to actually measure
• 26:59
  Speaker 2: this thing. So people built these tilt meters to try
• 27:02
  Speaker 2: to see, like, can you tell if the Earth is tilting,
• 27:06
  Speaker 2: Like if you have essentially a bathtub filled with water,
• 27:09
  Speaker 2: then the surface of the water tells you like where
• 27:11
  Speaker 2: gravity is all equal, and then if the surface of
• 27:14
  Speaker 2: the Earth tilts on which the bathtub is sitting, right,
• 27:17
  Speaker 2: there's like a wave that passes through the ground, it'll
• 27:20
  Speaker 2: tilt the bathtub and you'll see waves in the bathtub.
• 27:24
  Speaker 2: So people were using these like long tubes of water
• 27:27
  Speaker 2: looking for waves in them to see if they could
• 27:29
  Speaker 2: measure the earth tilting, looking basically for waves in the ground.
• 27:33
  Speaker 1: Interesting, So, like if you wanted to see New York
• 27:35
  Speaker 1: City when up a foot or not or more than
• 27:37
  Speaker 1: a foot, you would maybe put one of these tiltmeters
• 27:40
  Speaker 1: on the outskirts of New York City, so that when
• 27:43
  Speaker 1: New York City goes up, this thing would tilt and
• 27:45
  Speaker 1: would tell you, hey, new York City went up.
• 27:47
  Speaker 2: Yeah, exactly. These days, you can measure land ties most
• 27:50
  Speaker 2: precisely with gravitometers. Things are basically accelerometers. You can measure
• 27:56
  Speaker 2: the strength of gravity because you're measuring the acceleration of
• 27:59
  Speaker 2: the Earth Earth pushing up on you to overcome your
• 28:02
  Speaker 2: natural freefall. So essentially every accelerometer really is a gravitometer.
• 28:07
  Speaker 2: So the way they measure land tides now is they
• 28:09
  Speaker 2: measure how the gravity is varying, because as you get
• 28:12
  Speaker 2: further from the center of the Earth, your gravity decreases.
• 28:15
  Speaker 1: But doesn't the moon effect that gravity.
• 28:17
  Speaker 2: As well, it absolutely does. Yeah, So what you're measuring
• 28:20
  Speaker 2: is you decrease on your gravity from being further or
• 28:23
  Speaker 2: closer to the center of the Earth. And you're also
• 28:25
  Speaker 2: measuring the Moon pulling on you directly and the sun.
• 28:28
  Speaker 2: So you got to disentangle all of this stuff to
• 28:30
  Speaker 2: get the land tide effect out. But that's how they
• 28:33
  Speaker 2: measure it most precisely.
• 28:34
  Speaker 3: Now.
• 28:35
  Speaker 1: So like you're saying, like, my weight here on Earth
• 28:37
  Speaker 1: varies depending on where the moon is, not on what
• 28:40
  Speaker 1: I had for lunch. Yeah, all of those things.
• 28:44
  Speaker 2: All of those things absolutely. Yeah, the moon is pulling
• 28:47
  Speaker 2: on you differently based on where it is, so it's
• 28:50
  Speaker 2: like the tidal force on a joorghe directly. But then
• 28:53
  Speaker 2: also the Moon is changing the shape of the Earth,
• 28:56
  Speaker 2: which changes your distance from the center of the Earth,
• 28:58
  Speaker 2: which changes the earth gravity on you. And at the
• 29:01
  Speaker 2: same time, the Moon is pulling on the oceans, which
• 29:04
  Speaker 2: makes some of the oceans deeper or less deep, and
• 29:06
  Speaker 2: that also has an effect on the shape of the Earth. Right,
• 29:09
  Speaker 2: there's this like ocean pressure, this irregular loading on the
• 29:13
  Speaker 2: Earth also affects the shape of the Earth. And then
• 29:16
  Speaker 2: back and forth because as Earth itself gets squeezed by
• 29:19
  Speaker 2: the moon that affects the ocean tides, So a whole
• 29:22
  Speaker 2: thing is coupled in a really complicated way. Yeah, it
• 29:24
  Speaker 2: seems complicated. So then if you measure just the gravity,
• 29:27
  Speaker 2: how do you know what's doing what? You have to
• 29:29
  Speaker 2: have a model of all these things, and then you
• 29:30
  Speaker 2: can disentangle the various pieces as you measure how it
• 29:33
  Speaker 2: changes over time.
• 29:35
  Speaker 1: So then if the moon is directly over me, then
• 29:38
  Speaker 1: I'm going to weigh a little bit less? Am I
• 29:40
  Speaker 1: going to be able to feel that? Like, what's the
• 29:41
  Speaker 1: effect of the moon on me?
• 29:43
  Speaker 2: You could measure it if you had a very sensitive gravitometer.
• 29:46
  Speaker 2: The size the effect relative to the acceleration due to
• 29:48
  Speaker 2: Earth's gravity again is like one part in a million
• 29:51
  Speaker 2: or one part in ten million, So you need a
• 29:53
  Speaker 2: pretty precise gravitometer to detect this effect.
• 29:57
  Speaker 1: Well, I wonder you know, there's so much of biology
• 29:59
  Speaker 1: on Earth that is tied to the moon cycle, or
• 30:02
  Speaker 1: at least sort of tied to the moon cycle. Do
• 30:05
  Speaker 1: you think all of this biology is measuring the gravity
• 30:08
  Speaker 1: somehow or is it just going by moonlight?
• 30:10
  Speaker 2: I think you're absolutely right that a lot of biology
• 30:12
  Speaker 2: is tied to the tidal cycle and the cycles of
• 30:14
  Speaker 2: the moon. But I think that's because the local effects,
• 30:17
  Speaker 2: you know, the tide going up, the tide going down,
• 30:19
  Speaker 2: or there being more moonlight or less moonlight. I think
• 30:22
  Speaker 2: all these things are dependent on those secondary effects, not
• 30:25
  Speaker 2: directly on the gravity. But hey, I could be wrong.
• 30:28
  Speaker 2: You know, we recently discovered that birds have little quantum
• 30:31
  Speaker 2: mechanical sensors in their eyeballs that detect the magnetic field
• 30:34
  Speaker 2: of the Earth and help them navigate. So biology continues
• 30:37
  Speaker 2: to surprise us.
• 30:38
  Speaker 1: Yeah, we might have sensors within us that can detect
• 30:41
  Speaker 1: a millionth of a grammar or something of gravity changes.
• 30:45
  Speaker 2: Biology is amazing. I'll never understand it.
• 30:47
  Speaker 1: All right, well, those are land tides. Now let's get
• 30:50
  Speaker 1: into even bigger tides, bigger waves. Let's talk about galactic
• 30:55
  Speaker 1: tides what that means about our search for other planets.
• 30:59
  Speaker 1: But first, let's take an o quick break. All right,
• 31:13
  Speaker 1: we're talking about the tides, why they're high weather low,
• 31:18
  Speaker 1: And we talked about how the tides here on Earth
• 31:21
  Speaker 1: a fact, not just the oceans, but the Earth itself.
• 31:24
  Speaker 1: The Moon is squeezing all the rocks on Earth, changing
• 31:27
  Speaker 1: the shape of the Earth, making its rise and fall
• 31:30
  Speaker 1: and now Daniel, you're saying this also happens on a
• 31:32
  Speaker 1: galactic level.
• 31:34
  Speaker 2: Yeah, the motion of the Sun through the galaxy that
• 31:37
  Speaker 2: depends on gravity. It's being pulled by the gravitational center
• 31:41
  Speaker 2: of the galaxy, this huge black hole and all those stars.
• 31:44
  Speaker 2: It's also being pulled by lots of other stars. And
• 31:47
  Speaker 2: so the motion of the Sun through the galaxy is gravitational.
• 31:51
  Speaker 2: But our solar system itself is not a point object, right,
• 31:55
  Speaker 2: So the galaxy pulls differently on different parts of the
• 31:58
  Speaker 2: Solar system. The parts that are closer to the center
• 32:00
  Speaker 2: feel a stronger gravitational force than things that are further
• 32:03
  Speaker 2: from the center. And so the same way that like
• 32:06
  Speaker 2: the Moon is massaging the Earth, and of course the
• 32:08
  Speaker 2: Earth is massaging the Moon, and the Sun is massaging everybody,
• 32:12
  Speaker 2: the center of the galaxy is massaging our whole solar system.
• 32:15
  Speaker 1: WHOA, because I guess technically we're going around the galaxy
• 32:19
  Speaker 1: center sort of like the Earth is going around the Sun,
• 32:22
  Speaker 1: right exactly, Like we're trapped in the gravitational pol or
• 32:26
  Speaker 1: pull of everything in the galaxy, of.
• 32:28
  Speaker 2: Everything in the galaxy. Yeah, it takes about a quarter
• 32:31
  Speaker 2: of a billion years for the Sun to go all
• 32:33
  Speaker 2: the way around the galaxy, and it's like a thirty
• 32:36
  Speaker 2: million year cycle for it to go like above the
• 32:38
  Speaker 2: plane and below the plane. It's got this really funky
• 32:41
  Speaker 2: orbit around the center of the galaxy. But yeah, the
• 32:43
  Speaker 2: Sun is locked in gravitationally around the center of the galaxy,
• 32:47
  Speaker 2: and then gravity is massaging the Solar System. Remember the
• 32:49
  Speaker 2: Solar System is not just the Sun, right, it's also
• 32:52
  Speaker 2: the planets. So the Earth's or it gets tweaked a
• 32:54
  Speaker 2: little bit by this gravitational massage, which is one reason
• 32:58
  Speaker 2: we talked about, like the stability of the Earth's orbit
• 33:01
  Speaker 2: is important because there's all sorts of things like perturbing
• 33:04
  Speaker 2: it slightly. But on the outside of the Solar System
• 33:06
  Speaker 2: is this huge cluster of icy rocks called the ort cloud,
• 33:10
  Speaker 2: billions or maybe trillions of blocks of ice, which we
• 33:14
  Speaker 2: think are probably the source of long period comets. Commets
• 33:17
  Speaker 2: with periods like hundreds of years. The galaxies squeezing them
• 33:21
  Speaker 2: can perturb them, so they might be like in a
• 33:23
  Speaker 2: stable orbit around the Sun, but then they get pushed
• 33:26
  Speaker 2: to tying the little bit and they get tugged on
• 33:28
  Speaker 2: by other stuff and boom, now they're falling in towards
• 33:30
  Speaker 2: the center of the Solar system.
• 33:32
  Speaker 1: M I guess what you mean is like as the
• 33:35
  Speaker 1: Earth goes around the Sun in the Solar system, sometimes
• 33:38
  Speaker 1: it's closer to the center of the galaxy than it
• 33:40
  Speaker 1: is in other times in our orbit. And so that
• 33:43
  Speaker 1: you're saying the galaxies then is shaping our orbit here
• 33:46
  Speaker 1: of the Earth.
• 33:47
  Speaker 2: The galaxy definitely plays a role in the orbit of
• 33:49
  Speaker 2: the Earth and in its eccentricity. The Earth is pretty
• 33:53
  Speaker 2: stable in its orbit, as we talked about, but other
• 33:56
  Speaker 2: things are much less stable. They're lower mass, they're much
• 33:58
  Speaker 2: further from the Sun. It's unlikely that the galactic tides
• 34:01
  Speaker 2: are going to cause the Earth to plummet into the Sun.
• 34:04
  Speaker 2: Some little distant rock that's barely being held by the
• 34:07
  Speaker 2: Sun's gravity is much more likely to get its orbit
• 34:10
  Speaker 2: disturbed and then to fall in towards the center of
• 34:13
  Speaker 2: the Solar system.
• 34:14
  Speaker 1: Doesn't it depend on like the orientation of our Solar
• 34:17
  Speaker 1: system relative to the plane of the galaxy. Like at
• 34:20
  Speaker 1: the galaxy and our Solar system we're in the same plane,
• 34:24
  Speaker 1: then you would see a huge effect. Right, Like as
• 34:26
  Speaker 1: you go around the Sun, then sometimes you're really far
• 34:28
  Speaker 1: away from the galaxy the center of the galaxy. Sometimes
• 34:30
  Speaker 1: you're really closer. But let's say like our solar system
• 34:34
  Speaker 1: was more like a bicycle wheel going around the center
• 34:38
  Speaker 1: of the galaxy, then would it matter where in the
• 34:40
  Speaker 1: orbit you are, you would be almost the same distance
• 34:42
  Speaker 1: from the center of the galaxy.
• 34:43
  Speaker 2: Yeah, you're right. For things that orbit in the plane
• 34:45
  Speaker 2: of the Solar system, that is very important. And our
• 34:48
  Speaker 2: solar system is tilted relative to the plane of the galaxy.
• 34:51
  Speaker 2: How tilted, so there's like a sixty degree angle between
• 34:54
  Speaker 2: the plane and the galaxy and the planetary orbital plane,
• 34:58
  Speaker 2: so it's really quite tilted. It's not fully a bicycle wheel,
• 35:01
  Speaker 2: but there's like a sixty degree tilt there. But the
• 35:03
  Speaker 2: stuff in the orc cloud is not mostly in the
• 35:06
  Speaker 2: plane of the planets. The oor cloud is like a
• 35:08
  Speaker 2: sphere hasn't collapsed into a disk or into the plane,
• 35:12
  Speaker 2: and so that stuff is always feeling tidal forces. There's
• 35:14
  Speaker 2: always something closer to the center of the galaxy and
• 35:17
  Speaker 2: something further interesting.
• 35:19
  Speaker 1: So then and as you're saying, these rocks in these
• 35:22
  Speaker 1: asteroid belt are more sensitive because they're smaller, and so
• 35:26
  Speaker 1: then the galactic tidal forces can really make a difference.
• 35:29
  Speaker 2: There yeah, they're smaller, but also they're further from the
• 35:31
  Speaker 2: Sun and so the Sun just has less powerful hold
• 35:34
  Speaker 2: on them. And this is a big deal for life, right,
• 35:37
  Speaker 2: because commets plummeting towards the center of the Solar system
• 35:40
  Speaker 2: can be pretty deadly. One of them impacts Earth than boom, right,
• 35:44
  Speaker 2: mass extinction.
• 35:45
  Speaker 1: But also commets might bring water and things like that, Right,
• 35:49
  Speaker 1: those might be important then for life.
• 35:51
  Speaker 2: That's exactly right. We think that huge fraction of our
• 35:53
  Speaker 2: oceans may come from commets doing just that. So in
• 35:57
  Speaker 2: terms of like life evolving, you want a bunch of
• 36:00
  Speaker 2: galactic tides squeezing your work cloud so that you rain
• 36:04
  Speaker 2: down frozen comets onto newly formed planets so they get
• 36:08
  Speaker 2: oceans and form life. But then you don't want a
• 36:11
  Speaker 2: whole lot later on while that life is being incubated
• 36:14
  Speaker 2: and it's still fragile.
• 36:16
  Speaker 1: Well, speaking of life, also, aren't tidal forces in other moons,
• 36:20
  Speaker 1: for example, around the moons of Jupiter. Don't those effect
• 36:22
  Speaker 1: like the temperature of those moons, which might affect whether
• 36:26
  Speaker 1: there's life or not.
• 36:28
  Speaker 2: Absolutely we think that some of the internals of moons
• 36:31
  Speaker 2: around Jupiter are warm precisely because of these tidal forces,
• 36:35
  Speaker 2: and you're squeezing the entire planet, which causes friction inside
• 36:39
  Speaker 2: of it. Because you're massaging, you're changing its shape. It's
• 36:43
  Speaker 2: not just like it becomes a football and now it
• 36:44
  Speaker 2: moves like a football, which part of it is the
• 36:47
  Speaker 2: cone of the football is changing. So you're constantly squeezing it.
• 36:51
  Speaker 2: It's like you take cold dough out of the fridge
• 36:53
  Speaker 2: and you need it. It warms up, right, you're applying
• 36:56
  Speaker 2: energy to it. Internal friction.
• 36:57
  Speaker 1: Yeah, like if you massage a ball of clay, it's
• 37:00
  Speaker 1: going to warm up eventually.
• 37:01
  Speaker 2: Exactly. So some of these moons are warm on the inside.
• 37:04
  Speaker 2: We think they have liquid water oceans underneath a frozen
• 37:07
  Speaker 2: crust because of tidal forces, not because of internal heat
• 37:11
  Speaker 2: like the Earth, but because of tidal forces. Could be
• 37:14
  Speaker 2: keeping those moons warm and providing a place for life
• 37:18
  Speaker 2: here in our solar system or in other solar systems
• 37:20
  Speaker 2: whoa so.
• 37:21
  Speaker 1: In for example like Europa, right, which is the moon
• 37:23
  Speaker 1: of Jupiter. If there's life down there, basically their only
• 37:27
  Speaker 1: source of energy might be the tidal forces of Jupiter.
• 37:30
  Speaker 2: Yeah, exactly, and those are moon tides, I guess you'd
• 37:33
  Speaker 2: call them. Not sure, you're squeezing the whole Moon, and
• 37:37
  Speaker 2: that's where the energy comes from. Basically, you're extracting it
• 37:40
  Speaker 2: from the gradient of gravity of Jupiter, right.
• 37:43
  Speaker 1: Yeah, and they wouldn't see the Sun from underneath those
• 37:46
  Speaker 1: oceans in the ISO, like basically, Jupiter gravitationally would be
• 37:51
  Speaker 1: like their Sun.
• 37:52
  Speaker 3: Yeah.
• 37:52
  Speaker 2: I was just thinking about whether they'd also be able
• 37:54
  Speaker 2: to detect the gravity of the Sun. Imagine your life
• 37:57
  Speaker 2: that's formed under that ocean. You've never seen the star,
• 38:00
  Speaker 2: but if you're very sensitive to gravity, you might detect
• 38:02
  Speaker 2: the presence of Jupiter, and you probably eventually would detect
• 38:05
  Speaker 2: the presence of the Sun as well, perturbing effectively the
• 38:09
  Speaker 2: gravity of Jupiter. That'd be much more difficult than it
• 38:11
  Speaker 2: is here on Earth because Jupiter's gravity would be stronger
• 38:14
  Speaker 2: and the Sun's gravity would be weaker, so it'd be
• 38:16
  Speaker 2: a much more subtle effect than the Sun's gravity here.
• 38:18
  Speaker 2: But eventually those underwater scientists would figure it out.
• 38:22
  Speaker 1: Interesting, you mean those fishieses.
• 38:26
  Speaker 2: And that would make them tastier because of that knowledge.
• 38:30
  Speaker 1: Now, wonder if your fish that studies the stars, are
• 38:32
  Speaker 1: you astrophisies?
• 38:35
  Speaker 2: I think I'm finishist with this.
• 38:39
  Speaker 1: I'm just fishing for ideas here, Daniel, It's.
• 38:41
  Speaker 2: True that tides may power life underneath the frozen crust
• 38:44
  Speaker 2: of a moon. It's also possible the tides had a
• 38:47
  Speaker 2: really important role in the development of life here on
• 38:49
  Speaker 2: Earth and the development of life on other exoplanets.
• 38:52
  Speaker 1: Yeah, because I think scientists think that the tides had
• 38:55
  Speaker 1: a lot to do with how life evolved here on Earth, right,
• 38:58
  Speaker 1: or at least maybe how life got out of the oceans.
• 39:01
  Speaker 2: I hear a lot of different ideas, and all of
• 39:03
  Speaker 2: it's very speculative, all the way back to like the
• 39:06
  Speaker 2: actual formation of life itself from non life. That the
• 39:10
  Speaker 2: tides and the sloshing of all that water at the
• 39:13
  Speaker 2: shore helps like mix together primitive molecules that can come
• 39:16
  Speaker 2: together to make DNA or RNA or whatever, self replicating molecule.
• 39:21
  Speaker 2: Basically that the turbulence itself there was crucial biochemically that
• 39:25
  Speaker 2: you know, if water was just like static and sitting there,
• 39:28
  Speaker 2: it would take much longer for self replicating processes to
• 39:31
  Speaker 2: get going.
• 39:32
  Speaker 1: Meaning like the moon and the tides are a way
• 39:34
  Speaker 1: to steer the ocean kind of in a way which
• 39:36
  Speaker 1: in which you maybe kind of need in order to
• 39:39
  Speaker 1: just get life going. Makes it makes the right chemical.
• 39:42
  Speaker 2: I mean, nobody likes to be called a pot stir
• 39:44
  Speaker 2: but yeah, the moon is basically stirring the pot down here.
• 39:46
  Speaker 2: The Yeah, there's lots of different speculations. It might just
• 39:50
  Speaker 2: be the tub stirring. Some people think that having the
• 39:53
  Speaker 2: tides is like a way to concentrate solutions. Like you
• 39:57
  Speaker 2: throw water up on hot rocks that were sitting in
• 40:00
  Speaker 2: the sun, and then the water evaporates and you like
• 40:02
  Speaker 2: have concentrated all your chemicals so you can get like
• 40:05
  Speaker 2: more reactions in them. Lots of speculative ideas about what
• 40:08
  Speaker 2: it might have happened billions of years ago to get
• 40:10
  Speaker 2: life started, and then that speculation extends all the way
• 40:14
  Speaker 2: to like actually getting life out of the ocean. Some
• 40:18
  Speaker 2: people think that tide pools are a place that fish
• 40:21
  Speaker 2: learned to walk. Basically, being stranded in a tide pool
• 40:25
  Speaker 2: meant you better evolve some legs.
• 40:27
  Speaker 1: Well, you mean, like some fish we're hanging out by
• 40:29
  Speaker 1: the beach by the shore during high type, but then
• 40:32
  Speaker 1: when low tie came, they're like, oh, we're stuck here
• 40:34
  Speaker 1: in the land, and maybe we should learn to walk.
• 40:36
  Speaker 2: You know, that makes me wonder I never thought about
• 40:38
  Speaker 2: this do fish enjoy the beach the same way land
• 40:41
  Speaker 2: animals do. Do they go near the shore and they're like, ah,
• 40:43
  Speaker 2: this is so beautiful and relaxing.
• 40:45
  Speaker 1: Interesting, Like do they take vacations at the shore?
• 40:47
  Speaker 2: Exactly? Yeah, do fish take vacations at the shore? Deep
• 40:51
  Speaker 2: questions were uncovering today.
• 40:53
  Speaker 1: I think they kind of do, right, because in the
• 40:55
  Speaker 1: deep ocean they're more vulnerable to getting eaten, and there's
• 40:59
  Speaker 1: I think more food for them near the shore, So
• 41:02
  Speaker 1: it is kind of a kind of a result. It's
• 41:05
  Speaker 1: kind of a vacation spot for them.
• 41:07
  Speaker 2: Here a physicist and a cartoonist speculate, but marine biology.
• 41:10
  Speaker 2: But I think the actual idea speculative as it is,
• 41:14
  Speaker 2: is that land walking animals could have started as fish
• 41:17
  Speaker 2: stranded in tidepools. Not that like an individual fish of
• 41:20
  Speaker 2: course is going to sprout legs, but the fish that
• 41:23
  Speaker 2: have this ability to like scramble over a rock or
• 41:26
  Speaker 2: two are more likely to survive getting stranded in type
• 41:29
  Speaker 2: pool m.
• 41:30
  Speaker 1: Like maybe stranded one hundred fish or something. Most of
• 41:33
  Speaker 1: them died, but the ones that somehow had some weird
• 41:35
  Speaker 1: gene that let them flop around a little bit better
• 41:37
  Speaker 1: with their fins. Maybe those eventually evolved into the animals
• 41:42
  Speaker 1: that left the ocean and became us exactly.
• 41:45
  Speaker 2: And so having tithes on a planet really changes what
• 41:48
  Speaker 2: it's like for life to evolve there, to even start
• 41:51
  Speaker 2: from pre life organic molecules, and to develop. And so
• 41:55
  Speaker 2: when we look out into other solar systems for planets
• 41:58
  Speaker 2: that might have life on them, also very interested in
• 42:01
  Speaker 2: whether they have moons, stirring the pot down there on
• 42:04
  Speaker 2: the surface.
• 42:05
  Speaker 1: Well, like, maybe you're saying the only reason we have
• 42:07
  Speaker 1: life here on Earth is because we had moon. Like,
• 42:09
  Speaker 1: if we hadn't had a moon, maybe life wouldn't have started.
• 42:12
  Speaker 2: We don't know, it's just an equals one, but that's
• 42:13
  Speaker 2: a really interesting speculation. And if we go out there
• 42:16
  Speaker 2: and we search all these solar systems we find a
• 42:19
  Speaker 2: bunch of planets with moons that have life on them,
• 42:20
  Speaker 2: and a bunch of planets very similar but without a
• 42:23
  Speaker 2: moon and no life, then that would be a strong
• 42:25
  Speaker 2: argument that you need a moon to get life started.
• 42:28
  Speaker 2: But hey, most likely we go out there and find
• 42:30
  Speaker 2: something even weirder than we expected.
• 42:32
  Speaker 1: Mm, Like, maybe we're all moonies.
• 42:35
  Speaker 2: I don't know what that means, but it sounds good.
• 42:37
  Speaker 1: I mean, some parts of the Internet will be over
• 42:39
  Speaker 1: the moon to learn this truth. All right, Well, that's
• 42:43
  Speaker 1: another reminder that there are all these hidden forces all
• 42:46
  Speaker 1: around us, pushing and pulling us, and sometimes we're not
• 42:48
  Speaker 1: aware of the effects that they might have. But if
• 42:51
  Speaker 1: you look at the physics of it, if you look
• 42:52
  Speaker 1: at the details, maybe they have the ultimate effect, and
• 42:55
  Speaker 1: maybe they're responsible for life itself.
• 42:57
  Speaker 2: And the simple physics model of the Solar system of
• 42:59
  Speaker 2: just points orbiting each other with gravity isn't enough to
• 43:02
  Speaker 2: describe the reality of our lives. And in the origin
• 43:05
  Speaker 2: of life, everything is not just pushing and pulling on
• 43:08
  Speaker 2: each other. It's squeezing. It's tugging, it's massaging itself. It's
• 43:12
  Speaker 2: not just squeezing the ocean. It's actually squeezing our entire planet,
• 43:16
  Speaker 2: causing the crust of flex and stimulating earthquakes. But also
• 43:19
  Speaker 2: maybe the reason we're here.
• 43:21
  Speaker 1: Well, not just the Earth, it's also squeezing us technically.
• 43:23
  Speaker 2: Right, Yeah, that's true. Yeah, you have tides as well.
• 43:27
  Speaker 1: And does that mean the moon is actively chewing.
• 43:29
  Speaker 2: Me, It's trying to spaghettify it, turning.
• 43:33
  Speaker 1: Into pasta di slurt me up or to feed to
• 43:36
  Speaker 1: the fishes. Is all right, well, we hope you enjoyed that.
• 43:39
  Speaker 1: Thanks for joining us, See you next time.
• 43:46
  Speaker 2: For more science and curiosity, come find us on social
• 43:49
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• 43:53
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• 43:56
  Speaker 2: remember that Daniel and Jorge Explain the Universe is a
• 43:59
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