In short
Why lunar craters are nearly perfect circles (impact physics, “high-speed collisions,” and why meteorites sometimes survive), plus how Earth’s day length varies (sidereal vs solar day) and how timekeeping uses atomic clocks and leap seconds; then “size of life” explains how scaling affects strength, animal proportions, and why different forces dominate at different sizes.
Guests/backgrounds
No named guests appear in the transcript. The host is Neil deGrasse Tyson, with recurring co-host/producer “Chuck” (speaking during the episode).
Key claims
Craters are circular because impacts at sufficiently high speed cause an explosion that scatters debris isotropically, making angle irrelevant; Earth’s solar day averages to 24 hours but varies because Earth moves in an elliptical orbit; Earth’s rotation is slowing due to lunar tides, requiring leap seconds; limb strength scales with muscle cross-sectional area while body weight scales with volume, so larger animals need thicker legs; surface tension dominates for tiny organisms, enabling water-walking insects.
Notable examples
Meteor Crater (Arizona) renamed after impact theory; snowball “exploding” on walls; sundial “equation of time” up to ~14 minutes; cesium-137 atom defining the second; skaters pulling in hands to spin faster; ants lifting relative to body weight; water strider/“Jesus spider” walking on water; whale buoyancy; “Bugs Life” Bloody Mary scene.
Written by AI. May contain mistakes. Listen to the episode to check what was said.
Chapters
Tap a time to open that second in VOExploring Crater Shapes
2:24 to 2:58
Discussion on the round shapes of craters found on the moon
The Mystery of Circular Craters
3:01 to 6:14
Investigating why craters on the moon are predominantly circular
“Yeah, a picture of the moon, any photograph of the moon, what shape are the craters?”
Understanding High-Speed Collisions
6:14 to 12:12
Explaining the physics behind how high-speed impacts create circular craters
“Because volcanic craters, you punch up, it makes a hole.”
The Role of Atmosphere in Meteorite Impacts
12:18 to 14:00
How the atmosphere affects the impact and survival of meteorites
“When you throw a snowball at a wall, winter is coming up.”
Understanding Meteor Craters
14:00 to 15:12
Learn how meteor craters are formed and the evidence left behind.
“Yeah, you don't want to be leaving craters.”
The Length of a Day Explained
18:01 to 19:48
Uncover the true length of a day and the concept of sidereal versus solar days.
“Saturn is the only planet in the solar system whose average density is less than that of water, which means if you found a bathtub big enough, Saturn would float.”
Astronomical Factors Affecting Time
19:50 to 21:32
Discover how Earth's orbit and distance from the sun affect time measurement.
“So you're imagining with respect to the universe.”
The Influence of the Moon on Earth
21:34 to 26:51
Learn how the moon affects Earth's rotation and timekeeping.
“Oh, by the way, so the first day is a sidereal day.”
Leap Seconds: Keeping Time Accurate
26:55 to 28:00
Find out how leap seconds are added to adjust timekeeping with Earth's rotation.
“That's in response to earth slowing down.”
Understanding Leap Seconds
28:00 to 29:28
Learn about leap seconds and their impact on timekeeping.
“What I'm saying is we monitor when we have fell behind by a second.”
Show all 21 chapters
Earth's Rotation Influences
29:28 to 31:45
Explore how various factors affect the Earth's rotation.
“We toasted it with a sip of champagne and then went on our way.”
The Limits of Geoengineering
31:45 to 32:44
Discover the practical limits of using technology to alter Earth's rotation.
“then i had this diabolical idea we'd go set up jet engines um anchor them to the earth face them either due east or due west and ignite them.”
The Complexity of Timekeeping
32:44 to 33:18
Understand the complexities behind modern timekeeping systems.
The History of Time Synchronization
33:18 to 33:54
Delve into the history and evolution of synchronized timekeeping.
“synchronized clocks at the beginning of heist movies everyone had different time dude oh my god that's crazy oh man i wish i lived back then i'd never be late for anything it'd be like chuck You're 10 minutes late.”
Preparing for the Next Leap Second
33:54 to 34:34
Discuss the anticipation and celebration of future leap seconds.
“And I love thinking about it just because of how many different branches of the science and technological world had to come together to figure this out.”
Preparing for the Next Leap Second
35:41 to 36:10
Discuss the anticipation and celebration of future leap seconds.
“Labor Day weekend means extra time to relax.”
The Physics of Size and Strength
36:45 to 42:00
Explore how size affects strength and the physics of living organisms.
“Well, listen, the way I see it is this, okay?”
The Importance of Body Type in Climbing
42:00 to 44:35
Explore how body type affects climbing performance and the adaptations of large animals.
“Go to an egg colony to have these diet books.”
Whales and Buoyancy
44:35 to 45:40
Understand why whales can grow large due to buoyancy and the implications of weight in water versus land.
“You got to go back to our weight density and whatever.”
The Laws of Physics at Different Scales
45:40 to 49:20
Learn about how physics changes with size, particularly in relation to surface tension and small creatures.
“Not only that, the laws of physics don't all manifest equally at all size scales.”
Size Constraints on Life
49:20 to 50:56
Discover why there are limits to how big or small life forms can be based on physical laws.
“By the way, the galaxy is 100 ,000 light years across.”
Transcript
Automatic transcript. May contain errors.0:00Every discovery starts with a question. What if? Why? How? When it comes to education, Southern New Hampshire University has answers. Whether you want to build new skills or pursue a lifelong passion, SNHU has over 200 online programs to expand your horizons. And the flexible format lets you learn on your schedule without putting life on hold. So if you're asking, what's next for me? It's time to find out. explore what's possible at snhu.edu slash start talk that's snhu.edu slash start talk i grew up learning english at school and korean at home my husband grew up learning english at school and chinese at home and one of our good friends grew up learning english and speaking korean in school but speaking russian at home however i'm the only one who isn't fully fluent in the language i used to speak at home or still do with my parents i can speak okay but reading and especially writing is a whole other hill that I've been trying to be more intentional about, which is where Rosetta Stone comes in.
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2:16Neil deGrasse Tyson:by selecting work mode available on plus and pro plans thanks for showing up for these you know you know how i come up with them they're like things that people know about but they don't know as much as they think they should know or might want to know after they learned all they could know that was very dr seussian of you
2:43Neil deGrasse Tyson:Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now.
2:58Neil deGrasse Tyson:Something very simple, the shape of craters. Shape of craters? Yeah, a picture of the moon, any photograph of the moon, what shape are the craters? Well, they're all circle, concave little circles. They're perfect circles. Every single one of them. The big ones, the little ones, the medium ones, they are perfect circles. Okay? So. Let me guess. Let me guess. Aliens, just like on Earth, the same way they make the crop circles. They make moon circles. That's how they make the moon circles. moon circles there so yeah here's the thing it's interesting that as humans if there's something scientists don't understand people rapidly just go to god or aliens as well that's why they got the explanation for what all right it turned out it was a mystery why all craters are perfect circles for the longest time it was a mystery until about 100 years ago.
4:04Neil deGrasse Tyson:Okay. And let me tell you why it was a mystery. All right. So your first thought is well the moon doesn't have an atmosphere. Maybe it's getting slammed by meteors. Right. Okay. But is every meteor coming straight down at a 90 degree angle so that the explosion, when it hits it makes a is that? Surely some of them are at an angle. You'd expect some craters to be elongated. Right. And you'd have all sort of shapes from circle to very flattened circles. You'd expect that. Some of them would be divots. Like when you swing a golf, you know, it would just be like a. Oh, okay. Where it came in on an angle.
4:51Neil deGrasse Tyson:On the angle from, and with the, because you'd have a, the slope would be different on one side than the other. Than on the other. Right. Because it came, slid in. It slid in. So you'd expect that, and it is nowhere to be found on the moon. So this energized the geologists because we know that the dark areas of the moon is where lava has once flowed. Okay? Oh, cool. I think they call it basalt. It's dark and it's lava fields, all right? And by the way, the Apollo astronauts aimed for those places because they're flat. If you're going to go a quarter million miles and land sideways and fall over, that's it.
5:31Neil deGrasse Tyson:All right? So they found the flattest areas. And those are called seas. Before people knew that the moon didn't have weather like we have or oceans, these large flat areas were called seas. The Sea of Tranquility. Okay? That's where it gets its name. Nice. And all the seas were named after psychological states or physiological states. So there's a sea of fecundity. There's a sea. All right. Yeah, all right. So anyway, so they're flat because lava in liquid state flattens out, right? There you go. All right. So wherever there was a crater, it was round. So the geologist said it's probably not these asteroids because they'd have to all come in perpendicular.
6:13Neil deGrasse Tyson:They're probably all volcanic craters. Because volcanic craters, you punch up, it makes a hole. The hole is a circle. Right. Okay? You know, you can pull that off. So that's that's how it stood for the longest while until people saw craters on top of places where it didn't look like lava had flowed. Right. So how are you going to have a crater and no lava signature anywhere near it? What's up with that? And so this was a conundrum. I have a book from 1890, and it says, believed by many to be volcanic in origin, perhaps they're actually of asteroid impacts. We are not sure. Okay. By the way, it was that way for most of the 20th century until computers came along.
7:14Neil deGrasse Tyson:And you could simulate impacts. Nice. You want to simulate it. Okay. So here you go. You ready? If you have an impactor that comes in straight into a surface, it makes a circular crater. If you send it at an angle, it will make an elongated crater. Okay? This will happen. So they're saying, no, wait a minute. Let's send it in faster. turns out there is a magic speed with which you can send in an asteroid and on collision it will make a perfect circle no matter the angle it hits no matter the angle it hits correct and that speed okay this is this is what okay you ready let me guess let me guess 88 miles per hour.
8:09Precisely. The same speed that it takes to propel you into the future.
8:17Neil deGrasse Tyson:Because the flux capacitor. The flux capacitor.
8:23Neil deGrasse Tyson:Okay. 89 miles per hour. All right. So here's what's going on. Let's take a rock. And you can ask, why does the rock sort of hang together? Right. Why isn't it just decomposed into sand? Well, because there are molecules that are attached. All right. It's molecularly attached within itself. Right. Right. These are electromagnetic forces. You can, we know what they are. Okay. All right. You can add up how much energy is contained in all of these molecular bonds. okay and you can come write down that number and you say this rock is held together by this much energy you can do that okay okay all right uh some rocks are held together with not much energy like if you take a sort of a semi a kind of solid thing like a snowball or it's obviously get to that in a minute right okay like a sand ball right right that if you just sort of punch it the whole thing just crumbles back into sand but it holds its shape held together just for a little while not much energy is holding that together snowball another example not much energy is holding unless you like really pack it in and what you're doing is you're melting the snow and have it refreeze and that holds it up better we had a whole we had a whole explainer on the freezing and melting of ice so what you're really doing is saying to the other person you're having the snowball fight with, I hate you.
9:53I hate you even more. Even more. Because this is going to be a nice little ice ball you're not going to get hit in the face with.
10:01Neil deGrasse Tyson:So that helps. And if it's held together only loosely, you can't even throw it without the thing flying apart. Okay. So you can write down how much energy that is. Calculate it and write it down. Now, move the object through space or through the air. there's a kinetic energy it has and this is the energy of motion it's called kinetic energy there's a formula it's one half times the mass of the object times the velocity squared okay all right okay now the moment the kinetic energy that the object has exceeds the binding energy of the molecules, you have to ask, well, if the thing was going at that speed and then after it hits, it's going at zero speed, then what happened to all that kinetic energy?
10:56Neil deGrasse Tyson:It got pumped back into the object. Right. But that's more energy than what is holding the object together in the first place. Right. So if you have more kinetic energy than the binding energy of the thing that has the kinetic energy, it's going to explode. On impact, it explodes. Wow. So we call these high speed collisions. And it's not just, oh, because it's going fast. No, it is higher speed than the energy that's holding it together. So on impact, it's an explosion. And explosions happen in all directions. Now, is that because the moon has no atmosphere? Because that doesn't happen on Earth.
11:39So, so, so let's, I'll get to that in a minute.
11:42Neil deGrasse Tyson:Okay. Let me get to that. Just imagine the air is not a thing. Okay, imagine the air is not a thing. Energy. Just talking about the energy. Okay. Okay. All right. So, so there you have it. That's the entire reason. So in fact, all the craters on the moon, damn near all the craters on the moon, there might be one or two that were volcano. All the rest are asteroids, meteors coming in at whatever angle they choose. Doesn't make a difference. That doesn't make a difference. They all explode on impact. They explode on impact because they are coming in at what we call a high speed collision. Now, now let's look at snowballs.
12:21Neil deGrasse Tyson:You should try this. Okay. When you throw a snowball at a wall, winter is coming up. Okay. Right. We're recording this in November. So you throw it at a wall. When it hits the wall, it doesn't stay as a snowball. No, it explodes. It basically pops. It goes everywhere. It goes everywhere. And try this. Except for one little white dot that's stuck to the wall. One little white dot that's stuck. So you've done this before. Yeah, I have. This to all our Hawaii friends and other friends who don't have snowball fights. So try throwing it at different angles when winter comes. You will see that every time it explodes on impact and you see the scatter all around in equal directions.
13:04Neil deGrasse Tyson:That's because even at your speed, okay, you're not going hypersonic speeds. It's just the speed that you throw it. That's more kinetic energy than is the binding energy of the snowball. Right. So that's why a high-speed collision, you have to ask what's binding the object and how much energy does it have of motion. And it's the relationship of those two numbers that'll tell you if it's a high speed collision. So a snowball on someone's chest exploding is a high speed collision. Nice. That's super cool. Yeah. Yeah. Let's just hope, though, that you never throw a snowball hard enough to leave a crater in somebody.
13:50Neil deGrasse Tyson:We're going to have a problem at that point. That would be more energy than is necessary to explode the snowball at the other side. But correct. Yeah, you don't want to be leaving craters. All right. So let's get back to the atmosphere. Very important and interesting question. Okay. So now an asteroid comes and it sees the atmosphere. Right. Well, the atmosphere is going to slow it down a bit, isn't it? Okay. It's going to slow it down. If it slows it down enough so that its kinetic energy is less than the energy that binds it together, it will survive on impact. Right. We do find meteorites. We had the ITE after it's on the ground.
14:35Neil deGrasse Tyson:Meteor coming through the air. Meteorite. We find there are meteorites that make it to the ground. Okay? Wow. Right. We have them. They're there. They slow down enough. the brakes on them put the brakes on them and it did not completely explode now in the explosion there could be some pieces that remain intact just in the explosion so in meteor crater arizona which used to be called barringer crater and peep and geologists said there's got to be volcanic because it's a perfect circle but there's no volcanic activity in arizona right it's just there's no volcano for miles all right so that was a conundrum when we figured it out it got renamed Meteor Crater.
15:14Neil deGrasse Tyson:And those computer simulations were abundant in the early 70s when we were able to program computers in the science laboratories. So that asteroid, they were saying, well, where is the asteroid? If an asteroid did it, let's dig and find the big asteroid. All right. And so they dug and they didn't find anything because they didn't know that the sucker blew up. Okay. And so a person bought that land, a mining company bought that land on the expectation that they could mine the metals of the asteroid that must be buried deep in it and it was nowhere 90 of it vaporized on impact yes they're pieces that are scattered around and and those pieces are now in collections we have some at the museum but most of it is gone for that reason and that's why craters around there you go okay you know we keep doing this will run out of stuff to explain.
16:08That's like reaching the end of the internet, which I don't think it's going to happen.
16:14Neil deGrasse Tyson:Well, the end of Netflix movies, right? Right. The next film.
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18:00Neil deGrasse Tyson:Here's yet another fact from Lost in Space, the latest collaboration between StarTalk and National Geographic. Saturn is the only planet in the solar system whose average density is less than that of water, which means if you found a bathtub big enough, Saturn would float. If you like that fact, you can find 4 ,999 more in Lost in Space. 5 ,000 facts to help navigate the universe. Lost in Space is now available for pre-order wherever books are sold.
18:59Neil deGrasse Tyson:How long does Earth take to rotate on its axis? From what I've been told, 24 hours. 24 hours. Okay. In fact, we kind of defined 24 hours to mean that. Right. So that's how we divide up time. Okay. So as you might have guessed, it doesn't take 24 hours. It actually takes 23 hours, 56 minutes, and 4 seconds. okay really yes now wait a minute wait hold on so let me just be clear about what i mean 23 hours get rid of the entire just get rid of the entire solar system okay watch earth rotate okay and stand there and time it it will that spot that's in front of you will come back around in 23 hours 56 minutes and four seconds one full revolution okay okay that's called a sidereal day I like this.
19:51Neil deGrasse Tyson:Because sidereal means star, star day. So you're imagining with respect to the universe. Okay? Nice. However, we don't base our lives on when stars return to the same spot in the sky, in the night sky. We base our days on when the sun, which also happens to be a star, returns to its spot on the sky. Okay? It turns out that takes longer than 23 hours and 15. Why? I'll tell you why. Because in the time it took Earth to rotate 23 hours and 56 minutes, it actually moved almost one degree in its orbit around the sun. So it rotates back to where its previous line, but it has to turn a little bit extra.
20:38Neil deGrasse Tyson:A little bit extra to get back to the same thing. A little bit extra to put the sun back in the same spot on the sky. Right. And that's a little five minutes extra. That's fantastic. Oh my God, that's just, I love that. I've only just begun. So, that little extra four minutes. So I said we move a degree in our orbit each day. You know, I didn't just pull that out. How many days are there in a year? 365. Okay, and how many degrees in a circle? 360. Yeah, so it's about a degree a day. It's about a degree a day. Yeah, technically it's one degree and five, of 365ths of a degree. But it's basically a degree a day.
21:20Neil deGrasse Tyson:And in that degree, you have to turn that little extra. So just imagine you keep having to turn your head. Just a little bit more. Extra amount. Okay. Because you move just a little bit, so now you've got to look back just a little bit. Correct. That's cool. Well, let's keep going, okay? All right. Earth's orbit around the sun is not a perfect circle. Oh, by the way, so the first day is a sidereal day. The second day is a solar day. Gotcha. Okay? So for obvious reasons. And they're not the same. All right. Now, Earth's orbit around the sun is not a perfect circle. Right. Which means sometimes we're farther away, sometimes we're closer.
21:53Neil deGrasse Tyson:When we are closer, we are moving faster in our orbit than when we are farther away. Okay. Okay? That's how gravity works. so it turns out that extra four minutes is not the same if we're farther from the sun than if we're closer to the sun because we move more than our allocated fraction of a circle when we're close to the sun and less when we're farther away from the sun gotcha okay so the length of the solar day is changing continually throughout the year. Wow. And sometimes it's less than 24 hours. Sometimes it's more than 24 hours. So sometimes the sun gets to its highest point in the sky before clock noon.
22:49Neil deGrasse Tyson:Right. And sometimes it gets. So what we do is we just average that over the whole year and say, sun, you are average 24 hours. And there you go. Wow. By the way, if you ever look at sundials, there's a map on the sundial that corrects for the sun being early and the sun being late. You either add or subtract up to 14 minutes of the day from what the sun time reads in order to get your clock time. Wow. All right. Every sundial has it. So it's a figure eight. It's called an anilemma. It's got a name, an anilemma. But I don't want to talk about anilemmas right now. So what you have on your clock is the average length of a day over the 365 days of the year.
23:32Neil deGrasse Tyson:All right. So now we define that as 24 hours, each hour, 60 minutes, each minute, 60 seconds. Got it. Okay. Well, what is defining this? Well, it's the rotation of the earth. Right. Okay. Makes sense. Well, well, all right. Well, how stable is that? Even in the perfect average that we're taking. it's how well you'll never know will you because you're using earth to define the time frame right exactly if earth is your measure and you are slowing down you will never know this just there's no way to know it right okay now back when i was growing up watches they would boast this is how old i am they would say get this watch it's so accurate it's accurate to two minutes a month wow okay that that was like accurate that is not a good advertising okay well then it was because you know cheap watches were 10 minutes a month you'd have to reset you'd set your watch every day why do you think heist movies would always say let's synchronize our clocks right before they perform the heist that's cool they knew that the clocks there were not keeping good time earth was keeping the best time of them all okay so now you pose the question maybe earth is not the best typing device let's offload the responsibility of keeping time to something else like a vibrating atom so we did that that's the cesium so the cesium 137 there's a electron transition between two energy levels that has a very precise frequency.
25:11Neil deGrasse Tyson:Okay? Very precise. You can measure. What's good about that is any lab can get some cesium and measure this and then define the length of a second in their lab. Okay? Okay. When you do this, you multiply it by 60. You multiply that by 60, you get the hour. You multiply that by 24. You do this and you find out that Earth is slowing down? Well, you know, it's kind of old. I'm just saying. It's been added. It's tired. It's a long time. It's a tired Earth. If you're 4.6 billion years old, you might slow down a little bit too. You might be tired too. I'm just saying, you might lose a step on your day.
25:52Neil deGrasse Tyson:That's very sweet of you, Chuck. That's very geriatrically sensitive of you. So you only would know that Earth was slowing down once you offload it to something else that tracks time. Right. And what we found out is that the sloshing of tides on the ocean floor, on the beachfronts, actually works to slow down the rotation of the Earth. Oh, wow. Okay, because the moon is causing these tides. Right. Okay. And we're rotating faster than the moon is orbiting us. So the moon is tugging on tides backwards on our attempt to rotate. Right. Okay. So it's almost like there's a counterweight. A counterbalance, exactly.
26:44Neil deGrasse Tyson:Counterbalance that's pulling against us. Wow. So tides are slowing down the rotation of the earth. And in response, the moon is spiraling away from us by a couple inches a year. Okay. That's in response to earth slowing down. It all relates to what's called the conservation of angular momentum, but it's a big ballet. Okay? And so we've been slowing down. And Chuck, that's, so what we could do is say, let's redefine the second, the length of the second, so that we always have 24 hours and 60 minutes and 60 seconds. But that's messy. Right. Every year, here's a new definition of the second, folks.
Read the full transcript
27:21Neil deGrasse Tyson:Go to your lab, redefine the cesium atom. It's much easier to accept the fact that, you know, we're breaking up with the moon, but, you know, it's just taking some time. Breaking up is hard to do. Everybody has to be on the same page so the breakup can be as amicable as possible. So that's a nice way to think about it. So the way we compensate for this is we add a leap second. Oh, well, it has to be every four years then. No, no, no. No. Did I mention years at all? I'm talking about days, dude. Days. Every four days? No, no, no. No, no, no. What I'm saying is we monitor when we have fell behind by a second.
28:07Okay. So when the second, when we know that we've lost a second based on our atomic measurement.
28:13Neil deGrasse Tyson:Correct. Then internationally, we say time to throw in a leap second. Now we throw it in. By convention, we throw it in on June 30th or on December 31st. and we can throw in one at each time if we needed it. Okay. Since 1973 or four, something like early seventies, there's been 23, 24 leap seconds added to the calendar. Sweet. So when they're going to add a leap second, they choose which of those days it will be when they do so that final minute has 61 seconds in it. Nice. Yes. It's very cool. That's very cool. And so, so this is what we do. The longest minute of the year. Yes, it's the longest minute because it's actually 61 seconds.
28:54Neil deGrasse Tyson:61 seconds. Okay. So newspapers like having fun with this. They say, this year will be slightly longer than other years because you have to throw in the leap second. That leap second happens on Greenwich time. So for us, it would take place at like, I guess, 7 p.m. Right. Because we're five hours behind them. On the Greenwich Mean Time. Right. Greenwich Mean Time. Right. So I was at a dinner party once in the June 30th leap second. And 7 p.m., that's when you're having dinner. And I said, pause. I got out the atomic clock, and we just watched that sucker tick. 61 seconds went by. We toasted it with a sip of champagne and then went on our way.
29:31Neil deGrasse Tyson:Okay. Why are you walking around with an atomic clock? No, no, I have, wait, just, no, I have access. Don't just, let's not, just, I got people. Okay, right on. All right. So a couple more things. Other things that can change the rotation of the earth. not just the title, sloshing. Right. Okay. But here's one for you. Are you ready? Good. All right. You've seen skaters who want to speed up their speed. So what do they do? Their hands start out extended. Uh-huh. And they start with a slight rotation. They bring in their hands and they spin faster. Right. Right. What they've done is they've changed where the mass is relative to their rotation axis.
30:09Neil deGrasse Tyson:Right. So the farther away the mass is, the slower they're going to rotate. The closer it is to the rotation, the faster they'll turn. Right. Okay. If Earth has an earthquake and one of the continental slabs shifts north, okay, then there's mass on Earth's surface that used to be closer to the equator the day before and has now moved closer to the pole. That will have the effect of speeding up the rotation of the Earth. Right. Large animals that migrate, okay, will change where the mass of the earth is from the northern climes down to the south, and they're farther away from the rotation of the axis.
30:58Neil deGrasse Tyson:so not only does do tides affect the rotation of the earth my seasonal migration of animals affects the rotation of the earth and so does earthquakes so do volcanoes and anything else that's remapping the surface of the earth and you know what else to change it the melting of land glaciers uh-oh we're in trouble okay that you got uh antarctica has has land glaciers as and melts what used to be right there near the pole now melts and goes closer to the equator that will slow down the rotation of the earth because that's like the skater bringing their hands farther away right so all of these factors combined basically earth today has been increasing rather than in principle it could decrease depending on what's going on right then i i then i had this diabolical idea we'd go set up jet engines um anchor them to the earth face them either due east or due west and ignite them.
31:54Neil deGrasse Tyson:And then the exhaust would help speed up or slow down the earth. I thought we might do that. Then I did the math on that. And? And no, it's not going to work. It's not enough. It's just not enough. You would have made a good Bond villain, though. Yeah, it's just, you know, it's like Lex Luthor saying, let me create an earthquake to make these properties in California. So, yes, geoengineering on a huge scale. But in principle, you could do that. But if you take the greatest engines and fire them, the mass of the Earth is so huge. You just have essentially no effect. No effect at all. Yeah. So I'm just saying the rotation rate of the Earth is susceptible to all these small effects that can add up.
32:41Neil deGrasse Tyson:And we deal with it. We, you know, deal with it. We throw in leap seconds. 23 hours 56 minutes and four seconds that's our rotation rate to the stars they start it's exactly 24 hours on average and that average is changing right oh man that is that's so cool man yeah just to show you that that smart people think about this stuff yeah and solve it so you don't have to because everyone you just think everything or just it works oh the computer tells me what the right time is and everything in the bank knows what time it is and my gps we've got top people thinking about this stuff so before the atomic clock nobody knew what time it was that's why they synchronized clocks at the beginning of heist movies everyone had different time dude oh my god that's crazy oh man i wish i lived back then i'd never be late for anything it'd be like chuck You're 10 minutes late.
33:38Not according to my watch. And as far as I can tell, don't nobody know what time it is.
33:48I'm not 10 minutes late. You 10 minutes early.
33:50Neil deGrasse Tyson:That's what the problem is. So that's all I got to say. I mean, it's a fascinating thing. That is fascinating. And I love thinking about it just because of how many different branches of the science and technological world had to come together to figure this out. Sweet. Well, I got to go. I'm preparing for the next leap second. You're going to be like. So, all right, dude. By the way, if we have a leap second announced, we'll do a special show and maybe celebrate that. And I'll bring out my atomic clock and we can watch it. That'd be so cool. I'm all about it. Okay. Yes. and make sure don't forget the champagne because you said you had champagne the last time.
34:31So don't even try to skip out on the champagne. You didn't forget that. That's right. Okay, I'm just saying.
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36:13Neil deGrasse Tyson:Hi, I'm Ernie Carducci from Columbus, Ohio. I'm here with my son Ernie because we listen to StarTalk every night and support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.
36:38Neil deGrasse Tyson:Consider a few things. I want to talk about life. Well, okay. Yeah, it's relevant. And on size and life. Well, listen, the way I see it is this, okay? you know, size is a preference thing. Okay. And not all of us can actually, you know, be what some people might have as a preference. And, you know, why are you looking at me like that? Because why? Perhaps you've been told something about, you know, my ethnicity and maybe I'm supposed to be a certain way. Well, it doesn't necessarily happen that way for every person in my position and someone who looks like me. We are witness to Chuck digging himself out of a box.
37:31Neil deGrasse Tyson:So here we go. So you're in a room there, right? All right. It looks like a hotel room. All right. You can walk around on the floor. I can. If there were an ant walking around on the floor, it would be doing just what you're doing. Absolutely. However, an ant can go to the wall and then just walk up the wall. Right. How come you're not walking up the wall? Because I'm not Spider-Man. Okay. That's all. If I were Spider-Man, I'd be walking up the wall. Okay, because Spider-Man is imitating a spider. Yes, he is. Okay. But there are no spiders the size of humans. This is true. That can just walk up the wall.
38:09Neil deGrasse Tyson:Correct. All right, there's a reason for that. There's a very good reason for it. And it has to do with the physics of life. Nobody ever talks about it that way. People say, oh, it's the biology, this. you can talk any biology you want at the end of the day physics sets the rules take that biologist here's a little smack down for you you biologist physics sets the rules even in your world physics all right so it all comes down to this go ahead jack okay so um how strong are your limbs well the strength of your limbs is measured by the cross-sectional area oh god so that tells you how big your muscles are well you're just embarrassing me on every level today first we're talking about size now we're talking about skinny wrist thanks all right so just take any part of your body your legs and your arms take the cross-section and that tells you how big your muscles are and when you say have big muscles you're measuring sort of a circumference okay and that's that's related to the that's always the way you measure circumference of the air okay right so as you get bigger your strength will grow as you're the area of your muscles Right.
39:34Neil deGrasse Tyson:The cross-sectional area of your muscles. Okay. However, your weight goes up as the cube of those dimensions. Oh, my goodness. Now, of course, I knew your weight goes up, but I didn't realize that. Okay. Wow, that's a lot. That's okay. So that's why a 300-pound person does not look all that much bigger than a 200-pound person. Right. Okay? They're chubbier and they're big. If they could be tall, whatever. But if you start increasing depth, height, and width, as your volume increases, so does your mass. But your strength necessary to sustain that volume and that weight does not go up in proportion.
40:27Neil deGrasse Tyson:Right. So your limbs, if you're going to hold up a heavy animal, your limbs have to be much fatter than they would otherwise be if you were smaller. And what are your heaviest animals on Earth? Your elephant, your whale. On Earth's surface. The elephant. The elephant. Its legs are huge. Yes. Okay? They don't have spindly legs. No, they don't. Their legs are huge to compensate for the fact that strength only goes up as the area of their muscles, while the weight is going up as the volume. And volume rapidly outstrips area. Okay? Now, you can go the opposite direction as you get smaller and smaller and smaller.
41:18Neil deGrasse Tyson:the weight with your volume gets lower and lower and lower, and the strength of your limbs becomes better relative to your body weight. That's why an ant can lift, what is it? Not only is it why they can lift things relative to their body weight. Relative to their body weight. Okay, all right. Not only can they do that, it's why they can get around with really skinny legs. Right. Okay, yes, they have six of them, but they're really skinny compared to the thickness of their body. Because the legs aren't holding up much weight relative to their own strength. Right. And they intermittent fast. They do intermittent fasting, too.
41:57Is that how that works? Thank you. I'll take so.
42:01Neil deGrasse Tyson:Go to an egg colony to have these diet books. Wow. So you know what? You just you just gave me a really stark thought, which is I watched this documentary about this guy who climbed the only clip face that these people die all the time climbing without any belay. And this guy was super skinny. Yep. Yep. Not strong like with big giant muscles, but I mean, his muscles, when you look at his musculature, this dude was ripped. He's ripped, but he doesn't weigh very much. But he doesn't weigh much at all. Correct. Correct. And that's why in the movie Cliffhanger, which involved rock climbers and mountain climbers, it starred Sylvester Stallone, who's got all these muscles.
42:54Neil deGrasse Tyson:It's like, no, every mountain climber on earth knew that that is not the body type. because he's got muscles where he does not need them. He's got body mass that is counter to his ability to support himself. So the point is, generally, and there's certain exceptions depending on environments, the smaller you are, the less you weigh, the thinner your legs can be and still hold up your weight. And the bigger you are in mass, the thicker your legs are. So rhinoceroses and hippopotamuses, hippopotami, and elephants all have really thick legs. Because as they got bigger, if they kept their thin legs, they'd break their legs.
43:40Neil deGrasse Tyson:And that's the end of you. You get eaten and you leave the gene pool very quickly when that happens. All the lions are missing you. Remember what we used to do? Remember those elephants with the skinny legs, man? And we used to just find them lying around. Oh, they made such a delicious meal.
44:04Remember those days?
44:05Neil deGrasse Tyson:We would just walk out on the plane and we would find the elephants. Well, they'd be the elephants on crutches because they kept breaking their legs. Right. So, anyhow. Oh, snap. So that's why you don't find very tiny creatures with really thick legs. That's that. So because they don't need it. That's the point. Okay. So, so now that, so that's an important fact. Number one, whales are different because they don't weigh anything. Right. You got to go back to our weight density and whatever. I was just about to say, did we talk about that? I think we talked about that. No, we didn't, but they're buoyant because they're at a certain depth.
44:46Right.
44:46Neil deGrasse Tyson:So they don't have to hold up their own weight. That's why they can get so big. Right. Okay. So it's not fair to say, how much is that? Well, it weighs 400 tons. No, it doesn't. It weighs zero because it is neutrally buoyant in the water. And if you bring it onto the land, it will die because it cannot hold up its own weight. It cannot do anything in its own weight. So you cannot say it weighs that much because that's not where it lives. It makes so much sense because you've never seen a beach whale say, all right, I'm out of here. I'm good with the land thing. I tried to beach. I tried to beach.
45:26I'm going to roll myself back on in here. I'm good. You never saw that.
45:30Neil deGrasse Tyson:You never saw that. So they don't weigh anything. They don't have to hold up their own weight. So they're really not. So everything I'm describing is sort of in the air on Earth's surface. Okay. All right. So, but I'm not done. Oh, cool. Not only that, the laws of physics don't all manifest equally at all size scales. Interesting. Okay. So, if you're going to drink water, you'll put it in a glass and then you'll drink it like this. Right. Why do you put it in a glass? Why don't you just sort of pour it in front of you? Well, because it'll flatten out on the table and you'll make a mess. Right.
46:08Neil deGrasse Tyson:Okay. But suppose I am an insect. Again, suppose I'm an ant. Does an ant need a vessel in which to put the water in order for it to drink? No, because water beads up. There's a bead of water that does not continue to spread. It could just walk up and suck the juice right out of the bead of water until it's gone. Okay. Now, the producers and writers of the movie Bugs Life knew this. so when the mosquito went to the bar and ordered a drink and what drink did the mosquito order a bloody mary of course
46:52okay so bloody mary i just i just turned into my mother i can't believe you turn into your parents
46:59Neil deGrasse Tyson:that's right i turned into my parents oh my god okay so mary a bloody mary o positive okay and And so the bartender, which is another insect, I don't remember what kind, has a spigot, pours out a blob of Bloody Mary and plunks it down in front of the mosquito. And it's just a ball. Okay. Held up by surface tension. Surface tension is this sort of this imaginary film that exists on the surfaces of liquids that you have to sort of puncture that in order to fall through. but that's that sort of film actually contains it in small enough amounts surface tension is not strong enough to contain a big blob of water like this because gravity wins but when you're small enough gravity loses against surface tension surface tension wins they plop this drop of bloody mary in front of the mosquito mosquito put in its nose sucked it out and then that's that was the end of that scene this was brilliant and it's in that movie it's a pixar movie that people who new physics and chemistry writing the script for that movie.
48:06Neil deGrasse Tyson:So different forces operate when you're small than when you are large. And so that's why they have, there's something called, is it a Jesus spider, a water strider, sometimes called, there's one, something that's, that walks on the water swiftly. And in some regions, they call it a Jesus spider, I think. Anyway, because Jesus in the Bible walked on water. Right. Except Jesus weighs more than the surface tension would have held him up. So Jesus would have just sunk without some kind of magic or spirit or miracle. Okay? Right. Whereas if you're small enough. Well, maybe he had just giant foam sandals.
48:48Foam sandals. We didn't check. Right. He was the first person to wear the giant foam sandals. And they're just like, oh, my God, Jesus. It's a miracle. People misinterpreted it. Right.
49:00Neil deGrasse Tyson:They were like, hey. But go ahead. So all I'm saying is that if you're small enough, that surface tension, you don't weigh enough to break the surface tension. So then you can just sort of walk on the water as some insects do. So my point is, size is everything in this world. And you might say, well, could you have something really big? Like a life form the size of a galaxy? Probably not. Here's why. Because suppose you're that big. By the way, the galaxy is 100 ,000 light years across. Suppose you have your head itches, and then you send the signal to the brain, and then it goes to your finger, and you've got to bring your finger up to scratch your head.
49:46Well, that took about 30 million years. It took it.
49:53Neil deGrasse Tyson:it's going to take at least 100 ,000 years to get your arm to your head moving at the speed of light. And you're probably not moving at the speed of light. So you're not going to be able to respond to stimulus the way life needs to in order to thrive in an environment. So there's certain sizes above which are not realistic. So physics contains the largest and the small. By the way, you can't be so small that quantum physics prevents your molecules from binding. You can't be smaller than the sizes of molecules. Right. Because what are you at that point? Okay? If molecules comprise life, you can't be life that's smaller than a molecule.
50:40Neil deGrasse Tyson:It's just not – there's no – so the chemistry and physics contain all the realms in which you will find biology. And that's just the beginning of it. I'm giving you the basics of it, where that's the entry level sort of size and life 101. So there you have it. So Spider-Man, he's got the powers of a spider? No, not if he's that size. He doesn't. No, he doesn't. No, he doesn't. No, he doesn't. He can't. No. He basically just has the powers of a really good rock climber. Rock climber.
51:19Neil deGrasse Tyson:yes that's about it that's that's about it all right we got we got to go there good to have you always a pleasure neil degrasse tyson signing off bidding you keep looking
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From the publisher
Is there a limit to how small life can be? Or how big? Neil deGrasse Tyson and Chuck Nice break down why all craters on the moon are round, the scale to life, and why the length of the day isn’t 24 hours.
NOTE: StarTalk+ Patrons can listen to this entire episode commercial-free
here: https://startalkmedia.com/show/why-craters-are-round-size-of-life-the-real-length-of-day-tytyk/
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