WEBVTT - What is tidal locking? 0:00:08.520 --> 0:00:11.320 Hey, Kelly, I have a controversial question for you. 0:00:11.760 --> 0:00:14.840 Oh boy, coming from you that makes me particularly nervous. 0:00:15.280 --> 0:00:17.120 Is this another episode I'm gonna have to make sure 0:00:17.160 --> 0:00:18.279 my kids don't listen. 0:00:18.040 --> 0:00:21.520 To no, but it might cause some other kind of 0:00:21.520 --> 0:00:22.320 family drama. 0:00:22.560 --> 0:00:24.119 Okay, now you have my attention. 0:00:25.120 --> 0:00:27.720 Well, you know, since you're married to a cartoonist, I'm 0:00:27.760 --> 0:00:30.320 wondering if I'm allowed to ask you whether you're a 0:00:30.360 --> 0:00:32.400 fan of a different cartoon. 0:00:32.800 --> 0:00:36.040 Well, that depends if it's a rival cartoon or not. 0:00:38.560 --> 0:00:42.080 So I'm wondering if you have a favorite cartoon from 0:00:42.280 --> 0:00:43.080 the Far Side. 0:00:43.440 --> 0:00:46.080 Oh, I mean he hasn't updated for a while, right, 0:00:46.120 --> 0:00:48.440 I mean, I suppose he's still competition. But anyway, all right, 0:00:48.479 --> 0:00:50.519 let's see, let's see. Oh, so hard to pick so 0:00:50.560 --> 0:00:54.320 many favorites. So there's one where there's a slide, you know, 0:00:54.440 --> 0:00:57.640 like a kid's playground, and some spiders have built a 0:00:57.760 --> 0:01:02.840 net or a web along the bottom, and one spider 0:01:02.920 --> 0:01:05.760 is saying something like, if we can pull this off, 0:01:06.360 --> 0:01:10.080 we'll never be hungry again, nor something like that, And I, 0:01:10.480 --> 0:01:13.240 as an invert person, just thought that that was amazing. 0:01:13.240 --> 0:01:14.840 And of course I liked the like School for the 0:01:14.880 --> 0:01:18.200 Gifted the one that was on T shirts when I 0:01:18.280 --> 0:01:20.160 was a kid. What about you, Well, I have. 0:01:20.040 --> 0:01:22.120 To ask you. Do you see that Spider's eating a 0:01:22.160 --> 0:01:24.640 baby cartoon differently now that you're a parent? 0:01:24.920 --> 0:01:26.280 No, still hilarious. 0:01:28.040 --> 0:01:28.160 Us. 0:01:28.200 --> 0:01:30.559 I think your children should be terrified if they listen 0:01:30.680 --> 0:01:31.520 to this episode. 0:01:31.959 --> 0:01:34.959 Probably. Oh my gosh, poor kid won. The other day, 0:01:35.080 --> 0:01:37.959 I told her to go get a bowl in my office, 0:01:38.360 --> 0:01:40.520 and she thought it was going to have something like 0:01:40.600 --> 0:01:42.920 candy in it, but she accidentally picked up the bowl 0:01:43.000 --> 0:01:46.440 of dead insects that I found in the in the 0:01:46.480 --> 0:01:48.600 barn that I was thinking of pinning at some point, 0:01:48.720 --> 0:01:51.320 and they were all over my office, so she must 0:01:51.320 --> 0:01:53.160 have seen it and thrown it up in the air 0:01:53.840 --> 0:01:56.320 and they went all over. My kids are going to 0:01:56.400 --> 0:01:58.520 have very high therapy bills at some point, but I 0:01:58.560 --> 0:01:59.440 love them very much. 0:01:59.560 --> 0:02:01.800 I think that living in your house must be even 0:02:01.840 --> 0:02:21.360 weirder than the Far Side cartoon, almost certain. Hi. I'm Daniel. 0:02:21.400 --> 0:02:24.720 I'm a particle physicist and a professor at UC Irvine, 0:02:25.000 --> 0:02:28.640 and I don't think I've yet traumatized my children with insects. 0:02:28.840 --> 0:02:32.000 Hi. I'm Kelly Wiener Smith, and I study creepy crawley 0:02:32.080 --> 0:02:35.840 things at race university, and I'm traumatizing kids all the time. 0:02:36.080 --> 0:02:38.280 Education through trauma is set your strategy. 0:02:38.400 --> 0:02:40.400 That's a good way to make people remember stuff. 0:02:43.600 --> 0:02:45.400 Where you live out on the farm, but there's lots 0:02:45.400 --> 0:02:48.240 of access to creepy crawley weird things, and so I 0:02:48.280 --> 0:02:50.920 hope your kids are become ver acclimatized. 0:02:50.280 --> 0:02:52.960 To that I'm making them because it. 0:02:52.960 --> 0:02:56.359 Takes a brave soul to explore the nature of the universe, 0:02:56.480 --> 0:02:59.919 or even just your backyard, depending on what's slithering out there. 0:03:00.080 --> 0:03:02.280 So whether or not you turn your eyes down to 0:03:02.320 --> 0:03:04.639 the ground or up to the skies, there's a whole 0:03:04.680 --> 0:03:07.040 lot of stuff to wonder about, and so welcome to 0:03:07.080 --> 0:03:10.000 the podcast. Daniel and Jorge explain the universe in which 0:03:10.040 --> 0:03:12.720 we do all of that wondering. We think about everything 0:03:12.760 --> 0:03:15.519 that's between your toes and everything that your eyes can 0:03:15.560 --> 0:03:18.120 gather as you look up into the night sky. We 0:03:18.160 --> 0:03:20.200 think about what's on the moon, what's on the backside 0:03:20.240 --> 0:03:22.720 of the moon, and what's in the deepest, darkest depths 0:03:22.760 --> 0:03:25.080 of the universe. We chew all of it up and 0:03:25.120 --> 0:03:27.120 try to digest it and explain. 0:03:26.800 --> 0:03:29.080 It to you, and it's not always pretty. 0:03:31.240 --> 0:03:34.600 Sometimes the truth is just gross. My typical co host 0:03:34.639 --> 0:03:36.680 and friend, Jorge Champ can't be here today, so I'm 0:03:36.760 --> 0:03:39.360 very glad to have one of our regular guest hosts, Kelly. Kelly, 0:03:39.360 --> 0:03:42.440 thanks very much for joining us again and terrifying your children. 0:03:42.760 --> 0:03:45.320 Yeah, well, I hope I could terrify some people today too. 0:03:45.400 --> 0:03:46.520 Thanks for having me back. 0:03:47.560 --> 0:03:50.080 But today we're not talking about the weird, creepy crawley 0:03:50.120 --> 0:03:54.320 bits that are inside Kelly's pantry, strange as that might be. 0:03:55.680 --> 0:03:58.720 We are turning our eyes to the sky tonight. We 0:03:58.760 --> 0:04:01.600 are thinking about what's out there in the universe, and 0:04:01.640 --> 0:04:04.600 what we can see and what we can't see, and 0:04:04.600 --> 0:04:07.520 how the gravitational forces that have built the structure of 0:04:07.560 --> 0:04:10.720 our universe also limit what we can see out there. 0:04:11.040 --> 0:04:12.560 If you were a kid like me, then you spent 0:04:12.640 --> 0:04:14.280 a lot of time looking up at the night sky, 0:04:14.480 --> 0:04:17.680 not just absorbing the stars, but also gazing on the 0:04:17.839 --> 0:04:21.039 closest object that's out there, the biggest, fattest thing in 0:04:21.080 --> 0:04:24.040 the night sky, and that's, of course our moon. It 0:04:24.040 --> 0:04:26.720 has so many fascinating features to it, but one of 0:04:26.760 --> 0:04:29.640 the most interesting features is that you always see the 0:04:29.720 --> 0:04:33.400 same features. Cally, do you remember understanding this as a kid, 0:04:33.520 --> 0:04:36.320 or wondering about why you're always seeing the same bits 0:04:36.360 --> 0:04:36.880 on the moon. 0:04:37.320 --> 0:04:40.040 You know, I really wish you hadn't asked me that, 0:04:40.120 --> 0:04:43.479 because the answer is, when I was a kid, I 0:04:43.560 --> 0:04:46.440 didn't realize I was always seeing the same side of 0:04:46.440 --> 0:04:49.440 the moon. That hadn't really hit me until I think, baby, 0:04:49.640 --> 0:04:51.640 I was in college, and then I was like, wait 0:04:51.680 --> 0:04:53.960 a minute, and I guess it just wasn't I was 0:04:53.960 --> 0:04:57.760 looking down at the salamanders and not up at the sky. 0:04:58.080 --> 0:05:00.320 But so, no, that is not a question I had 0:05:00.320 --> 0:05:03.039 when I was a kid, but it should be. When 0:05:03.040 --> 0:05:03.760 did you learn this? 0:05:04.080 --> 0:05:05.960 I remember learning about it, I think when I was 0:05:06.000 --> 0:05:08.239 seven or eight, But you know, my dad was pretty 0:05:08.240 --> 0:05:11.080 into astronomy and into science, and so we talked about 0:05:11.080 --> 0:05:13.960 this kind of stuff. Something I'm still curious about, though, 0:05:14.200 --> 0:05:17.440 is when humanity understood that, or when humanity understood it 0:05:17.480 --> 0:05:22.080 was an interesting question, like did ancient Chinese astronomers, who 0:05:22.160 --> 0:05:24.120 spend a lot of time looking up at the moon 0:05:24.160 --> 0:05:27.520 and predicting its eclipses, did they figure out that the 0:05:27.520 --> 0:05:29.600 moon was a sphere and that it was rotating and 0:05:29.600 --> 0:05:31.920 that it was weird that we always saw the same 0:05:32.000 --> 0:05:34.920 side of it? Or is this just something they overlooked. 0:05:34.960 --> 0:05:36.359 Do you know the answer to that question. 0:05:36.640 --> 0:05:38.520 I don't know the answer to that question. I've been 0:05:38.560 --> 0:05:41.760 digging through the history of astronomy a little bit, and 0:05:41.839 --> 0:05:44.640 I know that Newton understood it because of his ideas 0:05:44.680 --> 0:05:48.000 of gravitation, But digging deeper into history, it's not really 0:05:48.000 --> 0:05:51.360 discussed very much. And I sort of wonder if people 0:05:51.400 --> 0:05:54.800 suspected that it was just a coincidence that the Moon 0:05:54.920 --> 0:05:57.360 rotates at this perfect rate just so that we can 0:05:57.400 --> 0:05:59.360 only see one side of it, because you know, there 0:05:59.400 --> 0:06:03.760 are other fascinating coincidences about the moon. For example, the 0:06:03.760 --> 0:06:06.440 moon and the Sun happen to be the same size 0:06:06.480 --> 0:06:09.560 in our sky, right, the Sun is much much bigger, 0:06:09.680 --> 0:06:12.920 but much much further away, and those two numbers line 0:06:13.000 --> 0:06:15.640 up perfectly. So the Sun and the Moon appear to 0:06:15.680 --> 0:06:17.600 be the same size, which is why we can get 0:06:17.640 --> 0:06:21.000 so many fascinating eclipse effects. And that, of course, is 0:06:21.120 --> 0:06:23.599 just a coincidence. There's no like deep reason for that. 0:06:24.000 --> 0:06:26.800 It just happens to be. These two numbers just kind 0:06:26.800 --> 0:06:27.960 of line up in our. 0:06:27.960 --> 0:06:33.160 Universe, and humans are notoriously tripped up by coincidences. 0:06:32.640 --> 0:06:35.839 Exactly, And so I think ancient astronomers must have wondered 0:06:35.880 --> 0:06:38.480 about that size, and I wonder if they also wondered 0:06:38.640 --> 0:06:41.560 about the rotation of the moon, if they understood that. Now, 0:06:41.600 --> 0:06:44.640 I do know that ancient Chinese astronomers had a little 0:06:44.680 --> 0:06:47.920 bit of a disadvantage compared to, for example, ancient Greek astronomers, 0:06:48.160 --> 0:06:51.320 because they didn't have geometry. Right, we think about the 0:06:51.440 --> 0:06:54.719 universe in terms of geometry. You imagine how clips has happened, 0:06:54.720 --> 0:06:56.320 and you think, probably in your head, you have a 0:06:56.360 --> 0:06:59.960 mental picture of all these things happening and to explain it. 0:07:00.240 --> 0:07:03.320 But Chinese astronomers didn't develop geometry, so they didn't have 0:07:03.400 --> 0:07:06.760 the same sort of geometrical thinking that we're all very 0:07:06.760 --> 0:07:09.680 familiar with. Instead, they had like tables of numbers, and 0:07:09.680 --> 0:07:12.440 they had arithmetic, and they could manipulate these numbers to 0:07:12.520 --> 0:07:14.680 do their predictions. So I think they must have thought 0:07:14.680 --> 0:07:16.560 about these things very differently than we did. 0:07:16.720 --> 0:07:18.640 Interesting, it's nice to have our modern tools. 0:07:20.360 --> 0:07:22.840 Thank you to those folks who invented geometry. It turns 0:07:22.840 --> 0:07:23.880 out to be pretty. 0:07:23.680 --> 0:07:25.480 Useful quote unquote modern. 0:07:25.760 --> 0:07:25.960 Yeah. 0:07:26.040 --> 0:07:28.360 Right, And so we have been looking up in the 0:07:28.400 --> 0:07:30.680 night sky and looking at the moon and seeing the 0:07:30.680 --> 0:07:33.720 same side of it for thousands and thousands of years, 0:07:34.120 --> 0:07:37.440 and now, of course we understand why. And so today 0:07:37.440 --> 0:07:39.400 on the podcast, we're going to be digging into the 0:07:39.440 --> 0:07:42.320 physics of the far side of the Moon and many 0:07:42.440 --> 0:07:46.520 other objects in our solar system that exhibit the same behavior. 0:07:46.880 --> 0:07:54.600 On today's episode, well, I answer the question what is 0:07:54.920 --> 0:07:56.160 tidal locking? 0:07:56.560 --> 0:07:59.040 And this is another thing that connects us to the dinosaurs, right, 0:07:59.040 --> 0:08:01.040 because they also would have seen the same side. 0:08:00.880 --> 0:08:05.480 Of the moon. If dinosaur geometers had figured that out, boy, 0:08:06.000 --> 0:08:07.440 they could have written a paper and got a lot 0:08:07.440 --> 0:08:08.160 of citations. 0:08:08.400 --> 0:08:10.240 They really could have, and then maybe they could have 0:08:10.280 --> 0:08:13.880 started a you know, NASA and had an asteroid deflection program. 0:08:13.880 --> 0:08:14.960 Everything could have been different. 0:08:15.840 --> 0:08:17.400 You sound like you're kind of hoping for that, but 0:08:17.440 --> 0:08:19.960 you know, in that scenario, we don't exist. 0:08:20.280 --> 0:08:21.280 Oh, good point. 0:08:22.040 --> 0:08:24.040 We're rooting for the asteroid on that one. 0:08:23.800 --> 0:08:24.800 That's right, we sure are. 0:08:25.280 --> 0:08:28.120 I'm sorry dinosaurs, which puts us on the anti math 0:08:28.280 --> 0:08:30.760 Education for Dinosaurs committee as well. 0:08:30.920 --> 0:08:33.559 It's an uncomfortable place to be, but no, it doesn't 0:08:33.559 --> 0:08:36.600 feel very good, but I'm firmly in this position. Yeah. 0:08:36.640 --> 0:08:38.760 So this is a topic that affects our Moon, and 0:08:38.880 --> 0:08:41.200 affects our planet, and affects a lot of things in 0:08:41.240 --> 0:08:43.599 the Solar system and in other Solar system. It's a 0:08:43.640 --> 0:08:46.440 fascinating little bit of physics. So I was curious what 0:08:46.559 --> 0:08:50.400 people knew about the topic of title locking and if 0:08:50.400 --> 0:08:52.480 they understood the physics of it. So I went out 0:08:52.480 --> 0:08:55.640 there into the internet to ask folks if they understood this. 0:08:55.800 --> 0:08:57.760 Thanks very much to those of you who participate in 0:08:57.800 --> 0:09:00.240 this segment of the podcast to let us know what 0:09:00.280 --> 0:09:02.880 people think about the topic of the day. If you'd 0:09:02.880 --> 0:09:05.160 like to hear your voice for a future episode, please 0:09:05.200 --> 0:09:08.760 don't be shy. Write to me two questions at Danielandjorge 0:09:09.200 --> 0:09:11.240 dot com. So think about it for a minute. Do 0:09:11.320 --> 0:09:14.600 you understand the physics of title locking? Here's what some 0:09:14.640 --> 0:09:15.880 listeners had to say. 0:09:16.120 --> 0:09:20.400 So, I believe that title locking is when, say, a 0:09:20.440 --> 0:09:23.199 planet has a moon that's locked in orbit at a 0:09:23.240 --> 0:09:26.320 certain distance, so the tides are always the same. So 0:09:26.440 --> 0:09:29.000 I guess you could say that we're in title locking 0:09:29.040 --> 0:09:32.520 because day in and day out, our tides go the 0:09:32.600 --> 0:09:33.320 same because. 0:09:33.080 --> 0:09:34.520 The moon's in a fixed orbit. 0:09:34.880 --> 0:09:37.520 Title locking is just like our moon. We see the 0:09:37.559 --> 0:09:40.000 same face of it at all times. 0:09:40.080 --> 0:09:42.520 It has no spin, and the dark side of the 0:09:42.520 --> 0:09:43.640 moon is facing outward. 0:09:43.800 --> 0:09:47.760 It is the deformation that a celestial body so first 0:09:47.800 --> 0:09:52.360 when it's orbiting or is orbited by another massive celestial body. 0:09:52.600 --> 0:09:57.319 Title locking is when a lower mass body is orbiting 0:09:57.480 --> 0:10:00.720 a much higher mass body and the the same side 0:10:00.840 --> 0:10:03.640 always faces it, so I know that we always see 0:10:03.679 --> 0:10:06.880 the same side of the Moon means tidally locked to 0:10:06.920 --> 0:10:07.280 the Earth. 0:10:07.679 --> 0:10:10.760 I was impressed that none of the listeners seemed totally 0:10:10.760 --> 0:10:13.920 stumped by this, because I feel like tidle locking is 0:10:13.960 --> 0:10:17.040 not necessarily something that you hear, like that at least 0:10:17.040 --> 0:10:20.080 there's a phrase I don't hear very often, and so like, 0:10:20.160 --> 0:10:22.959 it seems like some people knew exactly what you were 0:10:23.000 --> 0:10:25.439 asking about, and none of them were like me when 0:10:25.480 --> 0:10:27.880 I was a kid, and we're just totally unaware that 0:10:27.920 --> 0:10:29.199 this is a thing that was happening. 0:10:29.440 --> 0:10:33.040 Yeah, we got some pretty well educated listeners. The word title, 0:10:33.200 --> 0:10:36.080 I think makes some people think of tides, which is 0:10:36.120 --> 0:10:39.560 connected of course to tidal forces, you know, like the 0:10:39.600 --> 0:10:43.040 Moon pulls on the Earth and squishes its oceans and 0:10:43.360 --> 0:10:45.880 makes us have higher tides in some places and lower 0:10:45.880 --> 0:10:48.160 tides and other places. But that's not what we mean 0:10:48.200 --> 0:10:51.400 by title locking. Tidle locking is actually a different phenomena 0:10:51.640 --> 0:10:54.440 we're going to dig into today. But thank you very 0:10:54.520 --> 0:10:57.600 much to all of our volunteers. We really cherish your thoughts. 0:10:57.800 --> 0:11:00.360 Yeah, you have a smarter than average audience, I think, 0:11:00.440 --> 0:11:05.880 or smarter than Kelly average. I'm always impressed by the answers. 0:11:06.280 --> 0:11:08.199 They're smart and they're good looking too. 0:11:08.240 --> 0:11:11.920 That's right. I think that's called the halo effect. You 0:11:12.040 --> 0:11:13.719 know one good thing about them, and you assume you 0:11:13.760 --> 0:11:15.040 know all the good things about them. 0:11:15.120 --> 0:11:18.080 So let's dig into the physics of tidal locking. What 0:11:18.120 --> 0:11:20.120 it is, what's going on and why I play such 0:11:20.120 --> 0:11:22.880 a big role in what we see in our night sky. 0:11:23.160 --> 0:11:25.360 And I think the first thing to understand is just 0:11:25.440 --> 0:11:28.480 like the geometry of what's going on. Obviously, the Moon 0:11:28.800 --> 0:11:32.120 is orbiting the Earth, and the Earth is spinning, and 0:11:32.200 --> 0:11:34.200 the Moon is spinning around the Earth, and the Moon 0:11:34.280 --> 0:11:37.079 is also spinning on its axis. So there's sort of 0:11:37.200 --> 0:11:39.480 a lot of spinning going on. But you got to 0:11:39.520 --> 0:11:41.800 get all that spinning in your head to understand, like 0:11:41.920 --> 0:11:44.640 why we only see one side of the moon. 0:11:44.920 --> 0:11:48.640 Yes, so I am staring directly ahead trying to picture everything, 0:11:48.760 --> 0:11:50.800 So go ahead, what should I be imagining? 0:11:51.840 --> 0:11:54.439 So first, just put yourself on the Earth and forget 0:11:54.440 --> 0:11:56.480 the fact that the Earth is spinning, and just move 0:11:56.559 --> 0:11:59.480 the Moon around the Earth in your mind and imagine 0:11:59.480 --> 0:12:01.320 the Moon is like a shoe or something. If the 0:12:01.360 --> 0:12:03.960 Moon is not spinning, it's just orbiting the Earth, then 0:12:04.040 --> 0:12:06.200 the Earth is going to see different sides of the shoe. 0:12:06.240 --> 0:12:07.560 It's going to see the back of the shoe, it's 0:12:07.600 --> 0:12:09.679 going to see the front of the shoe, because as 0:12:09.720 --> 0:12:12.480 the shoe moves around the Earth, different sides of it 0:12:12.559 --> 0:12:15.000 are going to be closer to the Earth or closer 0:12:15.040 --> 0:12:15.880 to outer space. 0:12:16.120 --> 0:12:17.640 So the shoe is not rotating either. 0:12:17.800 --> 0:12:20.000 That's right. So first the shoe is not rotating, and 0:12:20.040 --> 0:12:21.319 so we see one side of it, and then we 0:12:21.360 --> 0:12:23.559 see the other side of it. So if the shoe 0:12:23.720 --> 0:12:25.960 or the moon or whatever is not spinning, then you 0:12:25.960 --> 0:12:28.440 would see different sides of it. Right now, the moon, 0:12:28.440 --> 0:12:31.280 of course, is spinning. It's spinning on its axis. But 0:12:31.360 --> 0:12:33.640 if it was spinning at some random rate, like really 0:12:33.679 --> 0:12:36.360 really fast or really really slow, you would still see 0:12:36.400 --> 0:12:38.599 both sides of it, because eventually it would spin in 0:12:38.679 --> 0:12:41.520 a way that revealed every part of the moon. The 0:12:41.559 --> 0:12:44.160 only way for us to not be able to see 0:12:44.200 --> 0:12:46.760 part of the moon is for its spin to be 0:12:46.880 --> 0:12:49.840 perfectly syncd up with its orbit, so that as it 0:12:49.920 --> 0:12:52.480 goes around the Earth, it turns just the right a 0:12:52.520 --> 0:12:55.560 mount every second, so the same side of it is 0:12:55.640 --> 0:12:58.440 always facing the Earth, like if the back side of 0:12:58.480 --> 0:13:01.320 the shoe is always fa the Earth, because the shoe 0:13:01.360 --> 0:13:03.480 itself is spinning at just the right rate as it 0:13:03.520 --> 0:13:04.880 goes around the Earth. 0:13:04.760 --> 0:13:07.680 And everyone on every part of the Earth is always 0:13:07.679 --> 0:13:09.760 seeing the same side of the Moon. Right, It's not 0:13:09.840 --> 0:13:11.760 like you know, in the US you see one side 0:13:11.760 --> 0:13:13.800 and in China you see the other side, or right, 0:13:13.880 --> 0:13:15.079 You're always seeing the same side. 0:13:15.160 --> 0:13:17.480 That's right. The same side of the Moon is always 0:13:17.520 --> 0:13:19.760 closer to the Earth, and the other side of the 0:13:19.760 --> 0:13:22.280 Moon that we call the far side, which I assume 0:13:22.480 --> 0:13:24.480 is the origin of the name of the far side 0:13:24.480 --> 0:13:28.520 and comic, it is always facing outer space. And this 0:13:28.600 --> 0:13:31.600 is the sort of coincidence we were talking about. Like these 0:13:31.640 --> 0:13:34.400 two numbers, the rate at which the Moon goes around 0:13:34.400 --> 0:13:36.640 the Earth and the rate at which the Moon spins 0:13:36.720 --> 0:13:40.320 around its axis have to be perfectly synced up to 0:13:40.360 --> 0:13:41.160 get this effect. 0:13:41.360 --> 0:13:44.040 And why are they perfectly syncd up? Is this one 0:13:44.080 --> 0:13:46.720 of the few instances in which we have something special 0:13:46.800 --> 0:13:49.640 going on and they just happen to sync up. Or 0:13:49.840 --> 0:13:52.680 are we just like every other moon because this happens 0:13:52.679 --> 0:13:53.240 all the time. 0:13:54.559 --> 0:13:57.280 So it's not that special and it's not a coincidence, 0:13:57.360 --> 0:14:00.439 but it's not something that's always happened. Like, to get 0:14:00.440 --> 0:14:02.760 into it, you have to understand the history of the 0:14:02.800 --> 0:14:05.040 formation of the Moon, like how did it get made, 0:14:05.280 --> 0:14:08.440 how was it spinning originally, and then how has that changed? 0:14:08.520 --> 0:14:10.840 You know, our moon is not just like some object 0:14:10.920 --> 0:14:13.600 that we captured as it was flying by. We think 0:14:13.600 --> 0:14:17.200 that the Moon actually comes from a huge collision something 0:14:17.280 --> 0:14:20.320 like one hundred million years after the Earth was formed, 0:14:20.320 --> 0:14:23.800 so we're talking like four point four billion years ago. 0:14:24.080 --> 0:14:27.120 You have some like very hot proto Earth. It got 0:14:27.160 --> 0:14:32.040 slammed into by some giant Mars sized planet they called Fea, 0:14:32.520 --> 0:14:35.200 And so you're talking about a huge collision like Earth 0:14:35.320 --> 0:14:40.000 versus Mars in space and both objects are essentially vaporized. 0:14:40.280 --> 0:14:42.400 But we still have thirst in the moon. 0:14:43.920 --> 0:14:47.320 You're like, how do that to current reality? You know, 0:14:47.400 --> 0:14:51.000 you're exactly right, it got vaporized, but then it coalesced. Right. 0:14:51.120 --> 0:14:54.320 Gravity is very very patient, and so even though all 0:14:54.360 --> 0:14:56.160 of its original work in the first one hundred million 0:14:56.200 --> 0:14:59.120 years was ruined by this collision. It got back to 0:14:59.160 --> 0:15:01.800 work and it pulled those blobs together and it made 0:15:02.000 --> 0:15:04.760 two new blobs, one that formed the Earth, and then 0:15:04.800 --> 0:15:07.160 a big ring around the Earth, like a ring of 0:15:07.200 --> 0:15:10.400 debris that was spinning sort of too fast around the 0:15:10.400 --> 0:15:13.440 Earth to fall into the central clump, which formed this 0:15:13.560 --> 0:15:15.480 like huge spray of material. 0:15:15.800 --> 0:15:17.680 All right, So, and that's why the Moon's made out 0:15:17.680 --> 0:15:19.160 of the same stuff the Earth is made out of. 0:15:19.360 --> 0:15:22.160 Exactly when we visited the Earth first and we sampled it, 0:15:22.360 --> 0:15:25.320 people were surprised to discover that it's basically the same 0:15:25.400 --> 0:15:27.920 mixture of stuff as the Earth. It's not like a 0:15:28.040 --> 0:15:31.120 different Solar System body that was formed in another place, 0:15:31.160 --> 0:15:33.320 and so it has a different mixture of like ices 0:15:33.400 --> 0:15:36.280 and rocks and different isotopes and stuff. It's basically made 0:15:36.320 --> 0:15:38.120 out of the same stuff as the Earth. And that's 0:15:38.120 --> 0:15:42.040 because it comes from the same mixture of those two planets. 0:15:42.520 --> 0:15:44.960 Like it was the same vaporized blob of stuff, and 0:15:45.080 --> 0:15:46.680 some of it fell in towards the Earth, and the 0:15:46.680 --> 0:15:49.160 stuff that was spinning around sort of too fast ended 0:15:49.240 --> 0:15:52.240 up in this big debris ring. But then gravity pulled 0:15:52.280 --> 0:15:53.800 that together into a moon. 0:15:54.160 --> 0:15:56.560 Did we have this hypothesis before we went to the 0:15:56.560 --> 0:15:58.560 Moon and found what it was made of, or did 0:15:58.640 --> 0:16:02.160 going to the Moon and physically collecting samples give us 0:16:02.200 --> 0:16:04.960 this hypothesis when we were like, whoa, it's the same stuff. 0:16:06.120 --> 0:16:08.400 This hypothesis has been around for a while, but it 0:16:08.440 --> 0:16:10.840 really became the favorite once we went to the Moon, 0:16:11.280 --> 0:16:14.400 and also once we understood something about the Moon's inner core. 0:16:14.800 --> 0:16:17.640 The Moon has sort of a small iron core, smaller 0:16:17.640 --> 0:16:20.480 than you would expect, and the hypothesis is that a 0:16:20.520 --> 0:16:23.440 lot of that iron was probably lost from when the 0:16:23.480 --> 0:16:26.000 impactor hit the proto Earth, and some of that was 0:16:26.120 --> 0:16:28.320 like melted and vaporized, and so it would have a 0:16:28.360 --> 0:16:31.440 bigger iron core otherwise. This became a much more popular 0:16:31.560 --> 0:16:34.080 hypothesis after we went to the Moon and visited and 0:16:34.160 --> 0:16:36.320 understood what it was made out of. And there's a 0:16:36.320 --> 0:16:38.720 lot of really interesting physics there that's relevant to it, 0:16:38.800 --> 0:16:41.760 Like why doesn't it all just collapse into a planet, right, 0:16:41.920 --> 0:16:44.680 Why doesn't it all just become one huge giant planet. 0:16:44.720 --> 0:16:46.760 How come part of it ended up as a ring? 0:16:46.840 --> 0:16:48.960 And that's just because you know, the whole thing is 0:16:49.000 --> 0:16:51.600 spinning and a lot of it has angular momentum, and 0:16:51.680 --> 0:16:54.240 so some stuff was just moving too fast to fall 0:16:54.240 --> 0:16:57.000 in the way, like the moon now is moving too 0:16:57.040 --> 0:16:59.640 fast to fall into the Earth. It's all about that. 0:17:00.520 --> 0:17:02.960 And then when that stuff gathered together into a moon, 0:17:03.160 --> 0:17:07.720 that stuff was spinning. So the moon had some original spin, right, 0:17:07.760 --> 0:17:10.239 that came from the spinning motion of all of that 0:17:10.359 --> 0:17:14.000 stuff after the vaporization. And we think that spin rate 0:17:14.080 --> 0:17:17.560 originally was much much higher than it is today. So 0:17:17.600 --> 0:17:20.640 the Moon used to be spinning faster than it is now. 0:17:20.800 --> 0:17:23.640 Was there this is maybe an unfair question. Was there 0:17:23.680 --> 0:17:27.280 anything alive on Earth when it was spinning fast enough 0:17:27.280 --> 0:17:29.560 that sometimes you'd see what is now the far side 0:17:29.560 --> 0:17:32.439 of the moon. So like dinosaurs probably never saw the 0:17:32.440 --> 0:17:34.600 far side of the moon, but did like the first 0:17:34.640 --> 0:17:36.560 bacteria see the far side of the Moon. I mean, 0:17:36.560 --> 0:17:39.080 I'm sure they don't see anything that far away, but 0:17:39.160 --> 0:17:40.119 you know, could they have. 0:17:40.640 --> 0:17:43.560 Yeah, it's possible. We don't really know exactly how old 0:17:43.640 --> 0:17:46.760 life is on Earth, but it stretches back billions of years, right, 0:17:47.240 --> 0:17:49.800 And so it's possible that there are critters that have 0:17:49.880 --> 0:17:52.240 lived on Earth that have seen other parts of the Moon. 0:17:52.280 --> 0:17:55.240 That's a very cool thought. Because the Earth has been 0:17:55.359 --> 0:17:59.720 gradually slowing down the Moon's spin little by a little 0:17:59.720 --> 0:18:03.679 every year, and the opposite is also true. But you know, 0:18:03.840 --> 0:18:08.080 until nineteen fifty nine, no human had ever seen the 0:18:08.119 --> 0:18:10.719 backside of the Moon. It was this like dark spot 0:18:10.800 --> 0:18:13.040 in our vision that we just couldn't see, no matter 0:18:13.280 --> 0:18:15.399 how many thousands of years we've been staring up at 0:18:15.440 --> 0:18:18.040 the Moon. Nobody had ever laid eyes on the backside 0:18:18.119 --> 0:18:21.920 until nineteen fifty nine, which feels really recent. 0:18:21.880 --> 0:18:23.399 Right, And the Soviets did. 0:18:23.280 --> 0:18:25.040 It, right, Yeah, they certainly did. 0:18:25.440 --> 0:18:27.840 Yeah, they beat us there with the lunar program. Their 0:18:27.880 --> 0:18:29.760 third one made it there. I think the first two 0:18:30.000 --> 0:18:32.480 maybe blew up. That was a thing that happened a 0:18:32.520 --> 0:18:36.600 lot for the Soviets. But anyway, so. 0:18:36.640 --> 0:18:38.880 Sorry, no, there's a really fun set of stories there. 0:18:39.040 --> 0:18:41.439 Maybe you know about because of your book research, that 0:18:41.480 --> 0:18:43.320 the Soviets were there first, and so they got to 0:18:43.440 --> 0:18:45.240 name a lot of stuff on the far side of 0:18:45.280 --> 0:18:47.600