Space Elevators, Skyhooks, and Space Fountains

9:23Hannah Fry:That's a baby. It's only got nine zeroes. This is like billions of times older than the age of the universe currently. Oh, billions of times.

9:32Michael Stevens:Yeah. 13.8 billion. You don't have to wait longer than the universe has even existed by a lot before any of this happens. But I'm saying there's a chance, okay? Sure. Yeah. If the earth is swallowed up by the sun, then congratulations, you will visit the sun in like seven or eight billion years. Just wait. It's a great way to travel through space. However, if earth is not engulfed by the sun, then it's got a lot longer before it gets to go on a special journey. In about 10 quadrillion years, if the sun does not suck up the Earth, in 10 quadrillion years, the Earth will likely be ejected from the solar system by some stellar remnant or something that's happened, something that's passed by our solar system.

10:23Michael Stevens:And to be fair, that doesn't really count as traveling through space because you'd still be on Earth. It's just that Earth would now be this lost planet.

10:30Hannah Fry:Wait, how did you get 10 quadrillion years there? Is that just like the

10:34Michael Stevens:probability that's just the probability yeah in in 10 quadrillion years the sun will just be this like dwarf star that will will still be capable of having things orbited it's not going to be producing the like warmth that anyone would like at all however earth could still be just like there as this like cold solid dead planet and your your grave could still be there you know Could still be like in memory of Michael Stevens and there's no one to read it. But, you know, it's still like it could be there. It could be there. Within 10 quadrillion years, we could get ripped out by some passing thing.

11:12Michael Stevens:And now we're going across the galaxy and Earth could go around the galaxy, taking us on this great trip for like 10 quintillion years. before probability says we will most likely have been ejected from the galaxy itself or fallen into a supermassive black hole.

11:32Hannah Fry:OK, because this is what happens to two kind of great big floating ice rocks. I mean, there are lumps of matter that are on that trajectory around the solar system, around the galaxy already.

11:45Michael Stevens:Now, astronomers and cosmologists have predicted these probabilities. We don't really know exactly when and how all this will happen, but we do know something about its likelihood. To recap, what I'm saying is if you wait a quadrillion, I may have been saying 10 quadrillion. It's, well, I mean, what's a factor of 10? Hey, among friends, in a quadrillion. These numbers are so estimated that going off by one magnitude of 10 in one direction or the other is like not really a huge crime.

12:16Hannah Fry:Well, also, I mean, you're talking about probability here, right? So you work out the chances of something like that happening, some intergalactic object knocking us off course and sending us off spinning into the galaxy. And it's an extremely small probability. And then you essentially work out how much time it would be for that probability to essentially be satisfied. But it could happen on day one. It could happen like, you know, in a couple of years' time. We don't know. It could happen during this podcast. Right. We can't be sure.

12:45Michael Stevens:We can't be sure. But within a quadrillion years, I'd put money on that bet. Yeah, right. There you go. So you have that to look forward to. Within a quadrillion years, your body will get to ride around on Earth through interstellar space. Even more exciting is that during this interstellar journey through the Milky Way, when Earth is just this lost rogue planet, within about 10 quintillion years, it's likely that we will either be ejected from the galaxy altogether. together or absorbed into a supermassive black hole. That is exciting.

13:22Hannah Fry:Here's what I think is cute about that is that you're still using the unit of years despite this period of time. The period when we were orbiting the sun was like a single eye blink at the birth of your existence, you know yes but still measuring things in years of the sort of acute archaic remnant of a long

13:47Michael Stevens:lost past i think cute is the right word because of course for these quintillions of years where earth is a rogue planet with no star there's no there's no year there's no sidereal year we're not orbiting around a star but i'm just imagining that there's like some really poor group of people who are like oh man what are we like they they took some immortality potion and now they're just stuck on this planet with no sun and they're like, oh, should we keep using years? I mean, there aren't seasons anymore, but it would be cute. You know, it'd be a little throwback.

14:20Hannah Fry:They could still be alive, though. If they if they harnessed, you know, the power of nuclear fusion and were living underground, they could feasibly they could feasibly still be alive.

14:30Michael Stevens:They totally, totally. That's a great premise for a sci fi novel. Now, whether that counts as visiting outer space, maybe not because you're still on a planet. But here's here's the final stage. It could be we're not sure yet, but it could be that eventually protons decay. Including the protons that make up your body. They could after a long it's going to be a long period of time because we've never like seen this happen. We can't be like, oh, the half life of a proton is, you know, 12 years like everything's always evaporating. Now, it's not totally agreed whether this will happen or not. There's a lower bound on how long it takes for a proton to have a chance of 50 % chance of decaying away into radiation.

15:19Michael Stevens:And it's huge.

15:20Hannah Fry:When you say huge, how huge are we talking?

15:22Michael Stevens:This is how huge I'm talking.

15:23Hannah Fry:Okay.

15:24Michael Stevens:According to the internet. I've heard of it. Within 100 undecillion years, all of your protons will have evaporated away as radiation.

15:38Hannah Fry:I don't even know what an undecillion is.

15:41Michael Stevens:Ah, good question. An undecillion is a one followed by 36 zeros. Okay. So 100 undecillion is a one followed by 38 zeros. Right. And that is a really exciting time that I'm looking forward to because at that point, I or my remnants are traveling on their own through intergalactic space as radiation.

16:07Hannah Fry:Well, because at that point, I mean, you will be muons, neutrinos, you'll be all of the subatomic particles. But hang on a second. If protons do disintegrate into subatomic particles, we know that you can get subatomic particles from them. because, I mean, that's what the whole idea of CERN is, right? Is that you take two protons and you smash them together and then you get this array, this kind of like scattergun of subatomic particles. But you're saying if they decay sort of without a high energy collision, well then doesn't that mean that everything is going to disintegrate?

16:43Michael Stevens:Yes. If protons decay, then the ultimate fate of the universe long after the heat death, long after energy is the same everywhere, meaning like temperature is the same everywhere and no work can be done, the universe will be cold for literally decillions of years before we start to notice, oh, things are leaving, like solid matter is radiating away. And then the universe will just be empty until another Big Bang happens.

17:15Hannah Fry:You know, you could at this point, you could absolutely make up a big number, a word for a big number. And I would just fully believe you. Oocillion, decillion, you know, you can make up your own one by now.

17:28Michael Stevens:The names of big numbers are awesome. Like there is a formula to it. And I made a short where I counted through all these names for, you know, for numbers. Every factor of a thousand. Yeah. Thousand, million, billion, trillion, quadrillion, quintillion, sextillion, septillion, octillion, nonillion, decillion.

17:50Hannah Fry:I'm okay with that. But where's eucillion? Undecillion. Undecillion. Sorry, eucillion is what you say to someone if they're being a bit of a woolly.

17:58Michael Stevens:You're basically saying the word 11. So it goes right after decillion. Undecillion and then treadecillion.

18:06Hannah Fry:Okay.

18:07Michael Stevens:I don't remember them all, but you can look this up. Like names of large numbers of ESOS might give you the short. It's very fun because I go all the way up to a Google. So there we go. There we go. somewhere between the blink of an eye and a hundred undecillion years. I feel like you're giving us quite a wide range. There's got to be a better way to get to space. So obviously the solution we're using right now is rockets. Rockets are expensive. They're noisy. They need to have a huge amount of just propellant as their mass, like 80, 90 % of their mass is just the fuel they need to get up into low Earth orbit.

18:50Michael Stevens:So that's also what makes them so expensive. You know, we've got reusable rockets now that have made this, you know, a little bit better. So using the Falcon Heavy, Falcon 9, it costs about two to three thousand dollars per kilogram to get something into space. Wow. Which means it costs millions to launch, you know, these rockets. But have we considered a stairway to space. Go on. Because you don't need to explosively go up. You can just slowly climb your way up. And to build a stairway to space, you got to first agree on where space is. I'm going for the KP line. Down to the KP line. But I'm going to go back because I want to take back something I said, which is we're not going to use the KP line.

19:39Michael Stevens:We're going to use the Carmen line because that's the one that I used for all my figures. I don't want to have five kilometers. They're pretty much the same. They're pretty much the same. So where is outer space? And the Kármán line is one of the most famous agreed upon definitions of that's where space begins. What is the Kármán line? It was proposed by Theodor von Kármán, who said, I think the best way to say where space begins is to say where airplanes stop, where aeronautics is replaced by astronautics. The difference being that below the Kármán line, there's enough air, the atmosphere is thick enough that a vehicle can travel with lift alone.

20:21Michael Stevens:It propels itself forward, smashes into enough air that it's lifted up and it flies like an airplane. Above the Kármán line, there's just so little atmosphere that lift is not possible and you've got to just be a rocket. So I think that's a great definition. And that line is, he calculated it to be about 80 kilometers above the surface of the Earth, but today it's set at 100 kilometers, 62 miles.

20:47Hannah Fry:So when you say, hold on a second, when you say you've got to just be a rocket instead, we're talking here that you have to be traveling fast enough that you're falling in the Earth's orbit, but the Earth is moving enough that it sort of catches you as you fall. I mean, that's essentially what we're talking about, right? Not yet, because I'm not talking about orbits.

21:05Michael Stevens:I'm just talking about getting to space.

21:06Hannah Fry:Wait, what do you mean when he says above this point, you can't be an airplane anymore, you have to be a rocket? What do you mean?

21:12Michael Stevens:I mean, you cannot go up anymore because of aerodynamic lift. The only way to keep going up is to throw propellant out and fly like a rocket. Got you. You cannot have thrust that moves you forward and then and then your wings hit the air and you go, oh, cool, I'm lifting up. You've got to just shoot the propellant down, thrust yourself up like a rocket. That line is traditionally set at 100 kilometers. To build a staircase that you could walk to get to the Kármán line would probably be pretty difficult. I don't know how much it would cost. Details, details. Those are just details. I do have one detail for you.

21:56Michael Stevens:If we assume that a step is the standard like 18 centimeters high, it would take 555 ,556 steps to get to space. Okay.

22:10Hannah Fry:And if you're doing 10 ,000 steps a day, we're talking two years.

22:15Michael Stevens:Well, yes, but that's like 10 ,000 steps a day tend to be just like steps forward. Steps up are pretty darn difficult. Like ignoring the effects of the thinning atmosphere, it would take a long time. So I looked up how quickly people can climb stairs. And to climb up to space, it's going to take like it's going to take more than three months for a healthy person who's really, really intent on doing this.

22:43Hannah Fry:Are they stopping to sleep?

22:44Michael Stevens:No, no stopping to sleep. This is just constant climbing. To put this in perspective, the tallest building on Earth, the Burj Khalifa, it's it's not 100 kilometers tall. It's 0.8 kilometers tall. And it has fewer than 3 ,000 steps, 2 ,909 steps. We need more than half a million steps to get to space.

23:05Hannah Fry:You also, in the UK, every 16 steps, you need to have a little landing that is at least as long as the stairs are wide. Yes. Maybe it's just in the UK, but building regs say it.

23:19Michael Stevens:This staircase that I'm imagining, it totally follows all regulations. Sure. It's got safe places for people to rest. I don't know how a human would do on this staircase. The best stair climber our species has ever created is Christian Roberto Lopez Rodriguez. This is a guy from Spain who has two world records for stair climbing. He climbed vertically on stairs, like on a stair machine, not on real stairs because we don't have tall enough ones. He climbed 18.7 kilometers vertically in 24 hours, over 70 ,000 steps. Okay. So he's a fifth of the way there. He did it in 24 hours. Right. And by the way, he wasn't climbing 18 centimeter stairs.

24:09Michael Stevens:He was climbing like 30 some odd centimeter steps, like twice as steep as normal ones. So Christian, you're our only hope. He also has the record for endurance, for just climbing stairs for an entire week. And listen to this. Listen to this. He climbed for a week and he managed to climb stairs for a vertical gain of 100.475 kilometers.

24:37Hannah Fry:Hello. Hello.

24:39Michael Stevens:Hello, Carmen Line.

24:40Hannah Fry:He passed it. It took him a week to walk to space. I want to see. What's his name? I want to see his thighs. What's his name? Christian Roberto Lopez Rodriguez. Let's have a look. He looks normal. Let me just make sure I'm looking at the right person because he also has the Guinness World Record for the fastest 100-meter sprint in stilettos. Wow.

25:04Michael Stevens:Let's get this guy on the podcast.

25:05Hannah Fry:Christian Roberto Lopez Rodriguez. Wow. He's from Spain. From Spain. He's only 3.24 seconds slower than Jamaican runner and eight-time Olympic gold medal winner Usain Bolt's 100-meter sprint world record. I suppose it's the same thing, really. Sort of like you're going up, aren't you? Your toes are up. Sort of same skill. Maybe we should do that. Maybe we should ask him when he is the first person to go to climb to space. He should do it in stilettos. Oh, yeah. Well, I'm sure he will.

25:34Michael Stevens:We just need someone to build the stairway to space first and then Christian Roberto Lopez Rodriguez. Off you go. You'll be the first. That sounds like a huge undertaking, climbing all of these steps, but But keep in mind, we're talking about 100 kilometers. Like it would take an hour to drive to space if it was a flat horizontal thing.

25:55Hannah Fry:What about a Stenner stairlift? One of the things that the elderly people get installed in their houses.

26:00Michael Stevens:Right. Why a stairway to space when it could be an escalator to space? Do you know what I mean? And so that's a perfect segue into what we should talk about next, which is, well, first of all, how we actually get to space. We use rockets. We use rockets because they you can just build one thing. You don't have to build half a million stairs, which like couldn't even stand up on their own. Like the scale of something that's of a building that's 100 times plus taller than the Burj Khalifa. We don't even know how to do that. But we know how to build a rocket that just uses propellant to blast itself up into outer space.

26:40Michael Stevens:However, rockets are really expensive and they're really loud and they're really dirty and they're pretty risky. So there's got to be something better. Right now, if you want to send a kilogram of mass to outer space using something like Falcon Heavy, Falcon 9, that's going to cost you$2 ,000 to$3 ,000 per kilogram. but there are ways that could be easier if we if we for example just built a escalator to space then you could just put your kilogram of material on the escalator and wait off you go it could cost like like literally a dozen dollars to get something into space i mean you can pack out

27:20Hannah Fry:that escalator have it as a conveyor belt you know people coming up people coming down it's easy

27:25Michael Stevens:The problem, though, is that generally we don't just want stuff or people to be in outer space. We want them to stay there and like orbit. And an orbit is very different than just being up really high. At the height of the International Space Station, gravity is still 90 % of what it is down here on the surface. So if I climbed a staircase all the way up 400 kilometers to where the International Space Station is, and then I stepped off, I'd fall back down to Earth. Like I wouldn't in order to orbit, I have to do something very, very different. And so I know you're familiar with this, but I'm going to talk about Newton's canon.

28:09Michael Stevens:Yeah. Which is, I think, a really great way to picture what exactly is going on when we talk about falling objects, orbiting objects and escaping objects. I wonder if you guys out there have seen the demonstrations of the fact that if you fire a gun horizontally forward on Earth and at the same time from the same height as the barrel of the gun drop a bullet. So when you drop one bullet, the other one gets fired out of the gun. Which one hits the ground first? Exactly the same time. Yes. Both of them hit at exactly the same time because the vertical acceleration caused by gravity is completely separate from the horizontal velocity given to the bullet by the gun.

28:55Michael Stevens:You might think, yeah, but what about like the isn't there some kind of lift that the air would give the moving bullet? And like not much because we've actually done this in real life and the bullets hit the ground at the same time. They don't hit in the same place. The one that you just drop, it falls down at your feet. the one you shoot, it's, you know, far, far away. But it's still only stayed up for the same amount of time.

29:16Hannah Fry:Next time we do some recordings in the States, Michael, I'm petitioning that we do this experiment live. We go to a shooting range. I want to do this live.

29:25Michael Stevens:Well, we should do that. And you know what? We should go down to Alabama and hang out with Destin from Smarter Every Day because he'll have the equipment. He'll have the locations.

29:35Hannah Fry:By equipment, I mean guns. Yes, yes.

29:36Michael Stevens:By equipment, I mean guns. Yeah.

29:39Hannah Fry:Yeah.

29:51Michael Stevens:This episode is brought to you by Cancer Research UK.

29:54Hannah Fry:When we talk about beating cancer, we often focus a lot on survival. And that can mean overlooking impacts that last long after treatment ends.

30:04Michael Stevens:Yeah. For example, take cancers in children and young people. the treatments themselves can be incredibly harsh. They can cause lifelong side effects like infertility or hearing loss.

30:15Hannah Fry:And Cancer Research UK is working to change that because young people, they should be able to grow up hearing the voices of the people that they love and living their lives to the fullest.

30:23Michael Stevens:That's right. And one clinical trial led by Cancer Research UK showed that giving another drug alongside chemotherapy nearly halved the number of children losing their hearing. And today, the treatment combination is being used by doctors across the world. For more information about Cancer Research UK, their research and breakthroughs, and how you can support them, visit cancerresearchuk.org slash restisscience. This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome? That's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50-page restoration block, or finally break down that long article you've had open for weeks.

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31:50Michael Stevens:Okay, so anyway, that's an important piece of physics to keep in mind. that these two different directions, down and forward, are independent. Just because you're moving horizontally doesn't mean you're falling any quicker or more slowly. But what if I made this gun fire the bullet faster? Well, then it will go a further distance, but it will still drop at the same rate. It'll still hit the ground in the same amount of time. If I keep increasing the speed of that bullet, eventually something really interesting comes into play which is the fact that the Earth is curved. Eventually, that bullet can be moving so quickly that it drops just like a bullet that I just drop out of my hand, but yet it's traveled so far horizontally that the Earth itself has also dropped underneath it.

32:41Michael Stevens:It's curved. Now, wait a second. If I get it just right, that means that I can get my fast-moving bullet to fall just as quickly as the Earth's curvature falls away from it. So it never hits the Earth. It just keeps falling forever. And that is what we call an orbit.

33:00Hannah Fry:That is what the International Space Station is doing, essentially, at all times.

33:04Michael Stevens:Exactly. Exactly. So the reason the astronauts in the International Space Station are floating around isn't that there's no gravity. There's a bunch of gravity. There's 90 percent of the gravity we're feeling right now up there. It's just that they are falling. They are falling, but Earth's surface falls away from them just as quickly, so they never hit it. Now, eventually, they do need to give themselves little boosts because there's a bit of air up there. There's enough that over the course of like a month, their orbit decays a bit and they come closer. They have to kind of boost back up. Instead of saying that there's no gravity, I like to just say that there's no G-force in the International Space Station.

33:42Michael Stevens:When you're in an orbit, when you're in free fall, there's definitely a lot of gravity. That's why you're falling. but there's no G-force, there's no weight, there's no feeling of weight and being pressed down against something.

33:52Hannah Fry:It's essentially the same trick as those vomit comets, you know, the parabolic flight things where they kind of go up and then drop and then go up and then drop. And when you're in free fall, you have the experience of zero G on your body.

34:05Michael Stevens:Yeah, exactly. As long as you're falling, you'll feel just like you're in the International Space Station. Problem is most of the ways we can easily fall don't last very long. oh yeah not without some sort of conclusion at the end okay so the reason i'm bringing up orbits is that uh when it comes to thinking of ways to get to space that aren't just rockets it's important that we not only come up with ideas that get us high enough get us up above 100 kilometers but also ideas that allow us to stay up there orbit the earth or even escape earth and go off to other places, the moon, Mars. Okay, so before we get into other non-rocket launch ideas, I want to talk about what kind of speeds are required for an orbit.

34:54Michael Stevens:The closer you are to the surface of the Earth, the faster you have to go because gravity is stronger.

35:01Hannah Fry:Like imagine, imagine that this exactly the same principle of Newton's cannon, but you're firing the gun and you're firing it so fast that it essentially orbits the entire earth before it falls.

35:14Michael Stevens:Yes. So how do you, how do you do, can I do that? Yeah, go on. Like on the surface of the earth? Well, as it turns out, no, but hypothetically, yes. So if you are six feet tall and you throw a baseball, it will eventually hit the earth unless you throw the baseball at 7 ,910 meters per second. That is the orbital velocity required for a circular orbit around earth at six feet altitude. So probably something's going to get in the way also like a tree or a mountain or another person's head. Probably a tree, a mountain, a person. But I'll tell you what will get in the way, air. Yeah. At that speed, at 7 ,910 meters per second, your baseball will last for the blink of an eye.

36:03Michael Stevens:It is going to explode into a fireball. But if we ignore the air, okay, then a baseball thrown at almost 8 ,000 meters per second, it's going to literally orbit the earth at human height. And so you could throw it forward and then wait a few hours and then get hit in the back of the head. Or you could catch it. You could play catch with yourself without having to just like throw the ball up. You can need quite a big mitt. is going very fast. It's going very fast because we're ignoring air resistance. So it's literally still going 8000 meters per second when it hits you. And also, if we're ignoring air resistance, how far will the ball have dropped by the time it gets back to you?

36:45Michael Stevens:Zero. It won't have dropped at all. It's in an orbit. But there's some good news here. If you go up higher, gravity is less strong. So you don't have to go nearly as fast to stay in orbit. If you went up to the top of the Burj Khalifa. Listen to this. Your baseball doesn't have to travel at 7 ,910 meters per second to orbit. It only needs to travel at 7 ,909 meters per second. Hey, they're coming down, Michael. They're coming down. I mean, literally, the speed the baseball needs to go is the speed that the ISS orbits at.

37:19Hannah Fry:Hang on, I've got it here. It's 7 ,670 meters per second. Whoa, 7 ,600.

37:25Michael Stevens:So 300 miles per hour less. I feel like I can throw a baseball that fast.

37:29Hannah Fry:Dropping, certainly be easier, wouldn't it? More achievable. Let's be clear though, right? The International Space Station is not blasting rockets out one side, pushing it 7 ,670 metres per second, right? When they sort of put it up there, you can basically put it into an orbital path where it effectively has the relative motion that it has in comparison to the Earth. So you're not like continually blasting rocket fuel to keep you going at that insane speed.

38:01Michael Stevens:No, no, you don't need to constantly blast fuel to keep yourself going fast up there because there's there's just not enough resistance from air. You're just kind of moving and your inertia has nothing to resist it. So you just keep going. And like I said, there is something to resist you. There is like a very, you know, sparse atmosphere there. So you do lose velocity over time. You are decelerated and you do eventually need to give yourself some boosts. I think we've talked about this on the podcast before. I've definitely talked about it in a short video before. But if like everyone on Earth just suddenly died from some huge catastrophe and the astronauts in the ISS were still alive, the first thing they would run out of would not be food or water or even air.

38:49Michael Stevens:The first thing they would run out of would be altitude.

38:52Hannah Fry:food right yes we did that they would slowly crash down to earth it all depends on how much

38:59Michael Stevens:fuel they have at that moment but they need regular deliveries of fuel for these periodic boosts usually like one or two a month um but they have more than that supply of of air water and food so yeah their their concern would be ah we're coming back down uh before they're like oh i'm hungry.

39:19Hannah Fry:Yeah.

39:19Michael Stevens:This this theoretical orbiting baseball idea on Earth is kind of disappointing. The baseball would get torn apart by friction with the air, like even if we devised a method to get it moving that quickly. But what we can do to do something fun like this for real is go to the moon because the moon has so much less gravity that standing on the moon orbital speed at six feet is only 1600 meters per second.

39:50Hannah Fry:Whoa. Okay. You could surely build a automatic ball pitcher that was able to do that. Surely.

39:58Michael Stevens:You surely could. I mean, and we already have. When I first looked this up years ago, there was like one gun that definitely could do it. And it was called the Paris gun. But since then, there have been some exciting developments in bullet speed, in projectiles.

40:15Hannah Fry:If this is going back to Destin and Alabama and Smarter Every Day's gun cupboard, I'm here for it.

40:22Michael Stevens:Well, yeah, maybe it should. Orbital speed, six feet above the surface of the moon is, just to reiterate, 1600 meters per second, more or less. And again, what that means is that you could throw a baseball or kick a football. Let's, you know, be UK about this. If you kicked it at that speed, straight forward at six feet up, it would go all the way around two hours. Approximately two hours later, it hits you in the back of the head. And if it didn't hit you in the head, it would just fly by you and it would keep going around the moon for for almost forever because the moon just doesn't have an atmosphere that's going to slow anything down.

41:03Michael Stevens:But I looked this up. I looked up like, what is the fastest bullet? And I found this YouTube channel called Banana Ballistics. It was fascinating. This guy was like, how fast can I get a bullet to go? And he you can you can go to his channel and it's literally the video is called like fastest bullet. You can go to his video to look up what cartridge and, you know, barrel length he was using. But he used a bullet that was made of brass and only weighed 12.5 grains. What how heavy is that? A grain is a seven thousandth of a pound. Whoa. OK. Which means this brass bullet weighed about as much as like four or five postage stamps.

41:43Michael Stevens:That's it. And he was able to fire it at Mach 4.7. Which is? Which is higher than Mach 4.6, which is orbital speed six feet above the moon.

41:56Hannah Fry:Oh, that's cool.

41:58Michael Stevens:So you could fire this bullet on the moon and then you got two hours to duck because that bullet's coming right back from the other side.

42:06Hannah Fry:it's probably not gonna do that well i don't know it's going pretty fast but i was just thinking about like if it weighs a few postage stamps how much damage would it actually be able to do but you know it does a lot of damage at 1600 meters per second that's the thing that's so amazing

42:20Michael Stevens:because it's it's going so fast that the physics are very different and he demonstrates in his video the difference between like a heavy bullet that's going at a normal speed and a tiny bullet going really fast. And the tiny one going really fast actually does more damage to like hard armored steel plates than the regular one. So that could, yeah, that's for a future episode with Destin. That's a fun little investigation of orbital speeds. But the most exciting orbital speed, especially for our purposes today, is the speed you have to travel at to orbit the Earth when you You are 35 ,786 kilometers above the Earth.

43:02Hannah Fry:Wait, why that number?

43:04Michael Stevens:That number is really special because the speed you have to travel at horizontally to not fall down to the surface of the Earth is exactly the same speed as the speed of Earth's rotation.

43:15Hannah Fry:Oh. So you are geosynchronous.

43:19Michael Stevens:You are orbiting the Earth, and yet you're not really moving around it. You are staying right above the same point on Earth's surface. You've got a geostationary orbit, essentially. That's what it is. That is geostationary orbital.

43:34Hannah Fry:How far did you say? 3 ,000?

43:36Michael Stevens:35 ,000 kilometers. That's insane. But yeah, I mean, International Space Station, 400 kilometers. Geostationary orbit, 35 ,000. I'm so astonished. Good fact. Or here's one of the things that's cool about a geostationary orbit. We put something up into a geostationary orbit. It's way up there, 35 ,000 kilometers up. It's not moving to the side or anything. It's just staying right above us. So if we dropped a really long ladder all the way down from that geostationary satellite, it would just like hang here. It wouldn't have to touch the ground. And we could just start climbing up this ladder, except not really, because that ladder and our weight on it is going to pull it down.

44:25Michael Stevens:Of course, because there's more gravity. We'll pull on all of that. Yeah. And so to counteract that, here's a quick idea. let's just put another cable, another ladder or tether coming out the other end of our geostationary satellite that's got a counterweight on it. Right. It's like an elevator. This is what we've talked about so many times on the podcast, the space elevator. Oh my gosh. It's literally a space elevator. Now the counterweight is further away than geostationary. So it's actually having to go faster. And the physics behind it is that it's trying to get flung out. If you cut the cable, connecting it to the rest of the elevator, it would fly off into a higher orbit.

45:11Michael Stevens:But when the whole thing is together, it just stays there. And so it's literally like a ladder or an elevator or a tether or whatever, whatever we make this structure be, a thing that goes all the way down to Earth. And then it doesn't even touch the ground. It can be, you know, it can be 10 feet above the ground. It could be 10 inches above the ground and it would just stay there and we could climb up it really not not climb but we could we could build little pods that mechanically climbed up it and could take all kinds of payloads all kinds of supplies people crews all the way up to the geostationary um uh little base and this would cost i mean it's hard to know what this would cost but it would be so cheap once you had it up and running once you had it up and running that's the problem it's going to be obviously a giant structure that you have to build it's going to be really expensive and um we currently don't

46:13Hannah Fry:know of any materials strong enough yeah i was going to say the tensile strength of the steel cable you're dangling down from 35 000 kilometers away it's gonna i mean that's gonna it's gonna

46:25Michael Stevens:take some engineering. The tensile forces of Earth pulling this down and then the counterweight trying to be flung into a higher orbit, that's so strong. There is a material that can do it and it's carbon nanotubes, but we currently don't know how to make them long enough.

46:41Hannah Fry:Right.

46:41Michael Stevens:So the space elevator concept, while really cool, while like literally if we figured it out, it would be a game changer. There would be human history before space elevators and human history after. It would be a turning point because suddenly going to space would be so much easier, a thousand times easier. We would basically have a road to space, okay? Which we don't currently have. Every other thing humans do, driving, sailing, flying, there's infrastructure. There are airports, there's roads, there's rails for trains, but we don't have anything, any piece of infrastructure that takes us to space.

47:16Michael Stevens:We just have the vehicle and it's got to just go. What have we been doing? What have we been doing? I think that we will. And I'm not 100 % convinced it's going to be a space elevator that we figure out because there are other things we could do already that would do the same thing, basically, would still be incredibly cheap. Like instead of$3 ,000 a kilogram for a launch, it'd be like 300, you know, maximum. So another idea is called a skyhook. And the skyhook idea is sort of like a a much smaller space elevator. It's just like a long tether that's in orbit and it can be in just low earth orbit, but it's rotating.

47:58Michael Stevens:So you got to imagine like a cartwheeling rope. If you're watching, I'm spinning my pencil around its middle and this is how it's orbiting earth while it spins. So it's like a circle rolling around the outside of another circle. If you imagine that, Then you can you can you can see how one point of it, the point that touches the ground is always sort of stationary for a moment. And then it zips back up. The idea here is that you would literally have a hook that kept swinging down into Earth's lower atmosphere and then flying back up and then coming back down. And it could come back down into like, I don't know, an airplane height.

48:38Michael Stevens:It doesn't have to come all the way down to where it's going to like hook onto a person. If you time it just right. If you timed it just right, you could jump onto this hook, which while it's just above Earth's surface pointing straight down, it's literally stationary for a moment. So you could just hop on. And then you're going to get whipped back up into space. We wouldn't have it come all the way down to the surface. You know, it could just be at like an airplane height. We could fly payloads up there, clip it onto the hook, and then, boom, they get like launched up into orbit. Obviously, you lose some energy when you do that.

49:11Michael Stevens:So the skyhook is going to keep needing to be kind of like boosted back up. But that's not necessarily that hard. If the skyhook is low enough, you can generate electricity from Earth's magnetic field because you're moving through Earth's magnetic field as a skyhook. And what do we know about moving through a magnetic field? Yeah. Electric current. Yeah. So we could power this thing. And it doesn't need to have a huge boost like we've got to have some big, you know, liquid fuel explosion. it can just slowly accelerate itself back to where it needs to be using Earth's magnetic field as an energy source and do all this work for us and launch things up.

49:51Michael Stevens:But my favorite, my favorite idea is a launch loop. A launch loop is a structure that we literally could make today. It would be very expensive, but we could make it. We've got the science for it. Go on. It would work. Like we don't even really need to do any demonstrations. We already know that this physics works. Building just a building that's really tall, that might not be very easy because the building has to support itself statically. But what if we built something that actively supported itself? What if we built something that was just a mega wild inflatable silly tube man? The way those things stay up is not because they're so strong.

50:37Michael Stevens:Yeah, they're not strong at all. They're being supported actively by air being blown into them. And those air molecules fly up and they eventually hit the sides and the top of the baggy structure and their momentum gets transferred and the thing stays up. Now, it wobbles around a bunch. So we would want to maybe not use air and wobbly materials.

51:00Hannah Fry:Oh, I thought you were going to say that in the arms, the arms are sort of being flung around a little bit. You could sort of jump onto one of them and get flung up. I'd be afraid though. Yeah. It's uncontrollable.

51:12Michael Stevens:I mean, maybe. Could you build an inflatable tube man with wobbly arms that are whipping around and they're whipping at a high enough altitude that they're not breaking themselves apart? That's the other concern. Yeah. And then you just have to grab onto its arm when it's low and then it'll whip you up.

51:28Hannah Fry:I like this idea of like a wind tunnel, sort of like a tube. You're pumping air in, which you're absolutely right. You could do. I mean, you could even have like sections along it that were where you added in extra air. I mean, you know, when you go indoor skydiving, when people do that, where you're sort of going into a wind tunnel and then it just blows you upward. I mean, that's basically what you're describing, right?

51:51Michael Stevens:Yeah. Yeah. Except instead of using air, we could use something even more massive. The concept of a launch loop is that you have a long tube and you evacuate the air from it. And how long, I mean, like hundreds of kilometers long, which is possible. And you would probably build this on like an island and it would go out over the ocean so that if it fell, it would just fall into the ocean. You then have, you evacuate the air from that tube so there's no air resistance. And you put a giant chain inside, like a big heavy metal chain. And you've got a mass driver on one end that just shoots this chain out through the vacuum of the tube.

52:29Michael Stevens:And you have magnets at the top of the tube that are deflected, repelled by this chain so that the chain's momentum actually keeps the structure up. Ooh, that's interesting. It's not having to support its own weight statically. It's actually being just like an inflatable tube man with air. it is a structure that can be dozens and dozens of kilometers tall because of this chain. And then the chain would come back down and it would be turned around, brought back, and then shot back up again. So this structure stays up because of this constantly moving, fast moving chain. And there can be redundant chains.

53:09Michael Stevens:And there are ideas that are more like space fountains where instead of a chain, you're just shooting up like giant ball bearings. So you don't have one big thing.

53:17Hannah Fry:But then hold on a second. How are you attaching planes onto the chain as it goes up?

53:22Michael Stevens:Yes, exactly. You're attaching them, well, not to the chain, but to the structure that surrounds the chain. And you could even electromagnetically be lifted by the chain's own momentum. And I haven't, I'm not the engineer who's done the math here, but you can lift a lot of weight this way and you can move it at the speed that you want, get it up high enough. It's certainly not orbiting, but you've gone so high that the amount of energy and the cost required to then get into orbit is a lot lower. Right. Now, I think building these types of superstructures shouldn't be sci-fi. I think we're really cheating ourselves out of something amazing by just saying, ah, well, no, we'll just keep building more and more rockets.

54:09Michael Stevens:I love rockets, don't get me wrong. But I think that one of the many things humanity needs right now is a giant piece of space infrastructure that will unite us all.

54:20Hannah Fry:A giant floaty man tube.

54:23Michael Stevens:A giant inflatable tube man thing. Yeah. In fact, the only comparable thing to the uniting effect of building a mega scale piece of space infrastructure would be something like the moon landing. I'll leave you with three quotes from people contemporaneously responding to what the moon landing meant to them, because I think it gives us a sense of what a launch loop could mean to humanity. Cool. When we landed on the moon, when humans first walked on the moon back in 1969, the New York Times reached out to all kinds of notable people to get their reaction. As you can imagine, almost everyone reacted with astonishment and wonder and pride.

55:10Michael Stevens:But Pablo Picasso was asked and he famously said, it means nothing to me. I have no opinion about it and I don't care. Obtuse as always, Pablo. I know. I love that because when you read through, you should look this up. You can look up the New York Times from the day after the moon landing and they have a whole section. It's like literally two or three pages of just here's what Jean Monnet said. Here's what the Dalai Lama said. And again, they're all really like IMAX narration, wonder of the world, planet Earth style things, except Picasso was just like, I don't care. And then let's not forget Charles Evers.

55:52Michael Stevens:He said the billions of dollars being spent on this moon exploration program means that it will be even longer before America begins to keep her promises to the poor.

56:03Hannah Fry:Yeah, which is always the counter argument, which is always the counter argument, which is the counter argument.

56:08Michael Stevens:So I've got these two counter arguments. Where should our priorities be and why should I even care? Right. But then this is what Paul Goodman said when he was asked how he felt about the moon landing in 1969. He said, it's good to waste money on such a moral and aesthetic venture. These meaning the rockets, the space infrastructure, the events, the adventures. They are our cathedrals. I don't think it is fair to say that they are our Roman circuses, for that is not the tone. We ought to see to it that people live well. But a part of living well is blowing money on big excitement, curiosity, entertainment and conversation.

56:56Hannah Fry:What better argument has there ever been for a giant inflatable tube man?

57:03Michael Stevens:Exactly. We need to ensure that everyone lives well. But we can't forget that part of living well is blowing money on huge, exciting things.

57:12Hannah Fry:I have that original copy of that newspaper downstairs in a frame, that exact article. Oh, do you really? I do, yeah.

57:20Michael Stevens:I've just been reading scans of it on the New York Times machine, which is beautiful, by the way, the Times machine. The Times machine. Every time I'm researching something, I go and I see what was being said at the time by newspapers.

57:35Hannah Fry:I was once doing a scientific debate at Cheltenham Science Festival with a couple of astronomers. and they were talking about the biggest events in history that science had given the world and they were arguing in favour of the moon landing, right? And I was, I think, in a bit of a contrarian mood and I don't know whether I should really share this out loud but I do wonder actually, apart from sort of awe and fascination, what has the moon landing ever done for us? You know, like, don't get me wrong. I'm the type of person who buys old newspapers reporting it and puts them on my wall. But, you know, if you compare it to sort of the invention of antibiotics or the discovery of antibiotics or, I don't know, like harnessing electricity or the invention of the computer even, you know, I think that there are like some really, really big scientific moments that have fundamentally changed the future of humanity.

58:35and this one sort of didn't.

58:39Hannah Fry:I mean, it did in an emotional way and it did in a sort of awe and wonder way and it did in a, this is what humanity can achieve kind of way. But I guess it speaks to the tension that you're describing there about, we need to take care of the poor before we do all of these crazy things. Because while I agree with you that actually space exploration is so endlessly fascinating, it's sort of, I want to know more, I'm completely in favor of literal blue sky research. I think this stuff is like really fundamentally important. I think you're right about how it brings us together as a species. I just also see the other argument.

59:15Hannah Fry:I do also see the other argument.

59:17Michael Stevens:And so do I. I think that the answer is that we need both. Because to say, well, besides awe and fascination, what did the moon landing do for us? is kind of like saying, well, look, besides keeping me safe and providing me with love, what has my mother done for me? She never gave me a job, you know. But that doesn't mean that I don't need a mom, right? Like we need antibiotics. We need each other. But we also need to have hope for our future. Agree. It can't be just one thing and not the others. But the whole package is part of what a good life and evolution means you know how there's all these i mean

1:00:03Hannah Fry:particularly billionaires who are really interested in colonizing mars it's like oh well the next step is and then we colonize the moon and then we colonize mars and so on i've just always found them something icky about that idea partly for exactly this thing that we're describing like why don't we actually just take care of our own planet first but secondly if you wanted to colonize an uninhabitable area, the Mugabe Desert is going to be way easier, right? Like the Sahara, that's an absolute doddle in comparison to sorting out the surface of Mars. I mean, aside from anything else, you've got an abundant atmosphere of oxygen and nitrogen, which is exactly what you need.

1:00:43Hannah Fry:The temperature might be a bit off, but everything else is there. Why wouldn't you? Why would you? But I think that there's something quite sort of sexy about these these space projects. There's something like very glamorous about it.

1:00:56Michael Stevens:If we built a human colony in a desert here on Earth, it wouldn't be very sexy. We would say, OK, but why did we do that? And colonizing outside of Earth is very much about that bigger idea of human freedom to be who we want to be. Like a colony on Mars is so separated from Earth that it can become a whole new society. It'll have its own passports, its own customs, its own culture in a way that isn't really possible anymore. Because, what, 200 years ago, the frontier closed. Like there just wasn't new space to go to. And so I think space exploration gives us that freedom again. But I also agree with the ick factor, and I'm really afraid for this in the future, which is that as space exploration becomes more and more of a private enterprise, it becomes something that doesn't belong to the people.

1:01:53Michael Stevens:The moon landing belonged to the people. If we want to use images from the moon landing on this podcast, we can do it for free because NASA's work is in the public domain because Americans paid for it. We bought it. with our tax dollars. But if I want to make a video about private spaceflight, I've got to talk through with with the legal teams there and I pay licensing fees and I can't get all the data. Whereas NASA is like, here's the transcript. We owe it to you. And that that's what scares me the most. I'm obviously very excited about space exploration as one of the many things we should be doing.

1:02:32Michael Stevens:But yeah, my biggest fear is that it has become a private thing for some against everyone else.

1:02:40Hannah Fry:I think we shouldn't be too romantic about the original moon landing, because that did happen at a time when the biggest question at the very forefront of everyone's minds, in America in particular, but across the globe more broadly, was nuclear weapons and missiles that could be launched from space, satellite technology, observation systems and so on. And so what was happening was the space race, you're right, was in the public domain, was on behalf of everybody, but it happened at this exact moment when those two things aligned, right? The sort of the need for defence and security in a military capacity aligned with the scientific goal.

1:03:27Hannah Fry:And I think that you're right that these two things now, it's become much more of a private enterprise thing, much more of a sort of almost a status thing, really. Yes. I mean, we're going back to Katy Perry now, aren't we, really? But more of a status thing because you don't have that entire nation sort of willing it forward in the same direction as the science, which I think was just the very particular circumstances at the time.

1:03:52Michael Stevens:That's right. Instead, it's being willed forward by commercial interests.

1:03:56Hannah Fry:Yeah.

1:03:56Michael Stevens:And this is what's also weird to me about AI. Not that this podcast is now literally covering everything. But at the end of the day, a lot of these LLMs are just corporate products. And it's not an individual. It's like a company is telling me what I want to know, as opposed to a friend who might have like worse ideas and less knowledge, but at least is a free individual. And so I feel that way about space exploration. Until I can take myself to space, I'm going to be beholden to something, whether it's a company or a nation, and they get to decide where I go and how and why. But the original pilgrimages were made by people who just used their own feet to go.

1:04:46Michael Stevens:And then they could establish a life that they wanted, not a life that fit the rules and regulations and corporate policies of the powerful. Yeah. Let us know down in the comments below and also on our subreddit. The rest is science. I want to hear what you guys think, especially about how do we prioritize these things? because everyone needs to be safe here. But at the same time, there should be hope for other things coming up. Does one need to happen before the other? Can they happen simultaneously and how? I don't know. I just know that all of these puzzle pieces make something really beautiful.

1:05:28Michael Stevens:And if we throw a piece away, then the puzzle won't be completed.

1:05:32Hannah Fry:Also, guys, giant inflatable tube man, you know, let's think about this more seriously. as ever send us anything you like the rest of science at goalhanger.com and we will see you next time see you next time

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