In short
Podcast Summary: The Rest Is Science - How To Fall To Earth (Without Burning Up)
Podcast Information
- Title: The Rest Is Science
- Hosts: Professor Hannah Fry and Michael Stevens (Vsauce)
- Episode Title: How To Fall To Earth (Without Burning Up)
- Episode Description: Exploration of the physics behind re-entry to Earth's atmosphere, the challenges of returning from space, and the surprising strategies used to prevent burning up during descent.
Overview
In this episode, Hannah Fry and Michael Stevens delve into the complexities of re-entering Earth's atmosphere. They discuss why it is easier to launch into space than to return safely, and they explore the scientific principles that govern this phenomenon. Through engaging discussions, they also address human psychology, superhero physics, and innovative engineering solutions.
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Key Concepts
- Re-entry Physics
- Velocity and Drag: Space shuttles re-enter Earth's atmosphere at speeds around 17,000 miles per hour, creating extreme temperatures due to friction with atmospheric particles.
- Shockwave Formation: As the shuttle turns broadside during re-entry, it generates a shockwave that creates a cushion of air, insulating the shuttle from extreme heat.
- Engineering Solutions
- Thermal Insulation Materials: Introduced the concept of using a material called LI-900 for spacecraft thermal protection, noted for being lightweight and excellent at insulating against high temperatures.
- Fragmented Design Approach: The space shuttle's protective tiles are not a single uniform covering; rather, they consist of 2,400 individual tiles to manage structural integrity and flexibility.
- Human Psychology and Fear
- Little Albert Experiment: Discusses the controversial experiment that conditioned a child to fear certain objects, highlighting ethical considerations in psychological research.
- Learning and Unlearning Fears: Introduces the idea of how fears can be unlearned, referencing behavioral therapy developments post-Little Albert.
- Superhero Physics
- Energy Costs of Superpowers: Explores the caloric energy required for superhero powers like super strength, flight, and super speed.
- Super Strength: Relatively low energy cost (e.g., lifting a tank requires about 280 calories).
- Flight: Requires significant energy (around 300 hamburgers per hour).
- Super Speed: Implies astronomical energy costs due to air resistance and kinetic energy, leading to hypothetical catastrophic consequences.
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Pivotal Moments
- Discussion on Little Albert: Michael reflects on the unethical aspects of the Little Albert experiment and its implications for understanding human behavior.
- Unique Engineering Challenges: Hannah outlines the complexities of designing re-entry vehicles that both withstand extreme temperatures and manage weight efficiently.
- The Historical Space Race Context: The episode discusses the competitive backdrop of the U.S. and Soviet space programs, emphasizing the importance of innovation in spacecraft design.
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Takeaways
- Understanding Human Limitations: The episode emphasizes the fragility of human life and the delicate balance of engineering and scientific knowledge necessary for space travel.
- Science Is Fun: The hosts convey a sense of curiosity and excitement about scientific exploration, urging listeners to embrace the complexities and wonders of the universe.
Additional Notes
- Support for Cancer Research UK: The episode is sponsored by Cancer Research UK, highlighting ongoing research and breakthroughs in cancer treatment.
- Engagement with Audience Questions: The hosts encourage listener participation by inviting questions and theories to explore in future episodes.
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For more information and to support Cancer Research UK, visit [Cancer Research UK](https://cancerresearchuk.org/restisscience).
Stay tuned for more episodes of "The Rest Is Science" to explore the fascinating intersections of science, curiosity, and knowledge!
Written by AI. May contain mistakes. Listen to the episode to check what was said.
Chapters
Tap a time to open that second in VOTeasing the Coolest Thermal Insulator
0:46 to 1:16
Discussion about the upcoming segment featuring a unique thermal insulator.
“Like, is it skateboard and wear sunglasses?”
The Little Albert Experiment
2:49 to 3:39
Discussion on the controversial Little Albert experiments and their implications.
“Well, look, our first discovery doesn't even come from Hannah or me.”
Understanding Classical Conditioning
3:40 to 4:41
Explaining classical conditioning through Pavlov's experiments and its relevance.
“I would have just gone there to stop it.”
The Ethics of Little Albert
4:42 to 6:10
Critique of the ethical implications of the Little Albert experiment.
“But the point is, we've heard of the Pavlovian reactions.”
Mary Cover Jones and Behavioral Therapy
6:11 to 7:45
Introducing Mary Cover Jones and her contributions to behavioral therapy.
“Point is, let's get back to the experiment.”
The Impact of Conditioning on Fears
7:46 to 9:03
Exploring how fears can be learned and unlearned through conditioning.
“And the one they chose was a white lab rat.”
Superhero Powers and Energy Costs
9:04 to 12:16
Discussing the energy costs of superhero powers through physics principles.
“And exactly as you describe, we didn't actually gain any serious or interesting scientific knowledge from.”
Caloric Efficiency of Human Body
12:17 to 14:03
Exploring the efficiency of the human body in relation to energy expenditure.
“So I knew what I was saying, and I was prepared to accept a fear of purple squares for life.”
Calories and the Human Body's Efficiency
14:03 to 14:30
Explore the efficiency of the human body in relation to calories burned.
“Go lift a tank and then you can earn yourself another.”
The Energy Costs of Superpowers
14:31 to 16:20
Understand the energy implications of super strength and flight.
“Well, it's also it's also the wrong way to think about it.”
Show all 25 chapters
The Science Behind Super Speed
16:20 to 18:09
Learn about the physics of super speed and its energy demands.
“I was wondering if you were going to factor that in.”
How Two Scientists Became Friends
18:09 to 21:32
Discover the story of how the hosts met and collaborated on a video.
“So we went from a Snickers bar to 300 hamburgers an hour to constant nuclear bomb explosions.”
The Impact of the Banach-Tarski Paradox
21:32 to 23:11
Delve into the complexities of the Banach-Tarski theorem and its implications.
“And I think up until that point, really nobody had delved into anything that complicated in a public forum, in a sort of, in a, something that was to be consumed by everybody.”
The Evolution of Educational Content
23:11 to 23:42
Discuss the growth of educational YouTube content and its audience.
“there's like one thing I wish I had done differently, which is the way I describe choosing the first set of points from the sphere.”
Thermal Insulation and Space Re-entry
26:25 to 28:00
Explore the history and challenges of re-entry vehicles in space travel.
“and use code TRIS for 20 % off your first test.”
Innovative Re-Entry Vehicle Designs
28:00 to 29:25
Learn about the evolution of re-entry vehicle designs and the genius behind them.
“You're squashing this air so rapidly with such a force that the temperatures that you start reaching are way higher than basically any human-made product could withstand.”
The Concept of Backwards Thinking in Aerodynamics
29:25 to 31:26
Discover how unconventional ideas transformed spacecraft design during re-entry.
“So his idea was, what if, what if instead of making it streamlined, you just deliberately make it as unstreamlined as possible, right?”
The Material Behind Space Shuttle Tiles
31:26 to 33:33
Explore the unique properties of the material used for space shuttle thermal protection.
“and people turning it upside down and going for the most un-aerodynamic space possible.”
The Fragility and Strength of LI-900
33:33 to 35:34
Understand the paradox of the LI-900 tile's fragility combined with its thermal resistance.
“It was invented by Lockheed Missiles and Space Company.”
Engineering Challenges of Space Shuttle Tiles
35:34 to 38:08
Learn about the complexities of using multiple tiles on the space shuttle.
“And I got really scared because I'd had my babies in this house, sort of sleeping next to asbestos walls.”
The Complexity of Re-Entry into Earth's Atmosphere
38:08 to 40:15
Discover the challenges of returning to Earth safely from space.
“and then every single tile on top had a unique shape, right?”
The Myth of the Moon Landing
40:15 to 41:38
Examine the intriguing arguments surrounding the moon landing's authenticity.
“I love it too, because we talk so much about to leave Earth, how hard it is to leave, to have the delta V required to leave our cradle.”
Technological Achievements in Space Exploration
41:38 to 42:00
Discuss technological marvels in achieving the moon landing and its implications.
“Have you seen that video where the guy shows that in 1969, it would have been easier to have gone to the moon and come back than it would have been to create a broadcast of that length, like a pre-recorded film segment.”
The Moon Landing Debate
42:00 to 43:18
Exploring the complexities and arguments surrounding the authenticity of the moon landing.
“Yeah, I think, you know, I sort of vaguely do remember he was talking about the size of the reels, like the physical size of the reel of tape, right, if I remember rightly.”
Safety Concerns on Carcinogenic Exposure
43:18 to 43:38
Discussing the safety levels of exposure to potential carcinogens in a lighthearted context.
“I mean, I just don't believe in humans that much.”
Transcript
Automatic transcript. May contain errors.0:00Hannah Fry:Welcome to The Rest of Science. This is Field Notes, sort of podcast expedition, if you will, where Michael and I, we trade the strange and curious objects that are filling our shelves and occupying our minds.
0:13Michael Stevens:And we answer the questions that are troubling yours.
0:17Hannah Fry:Every week, one of us is going to bring a sort of strange and spectacular object onto the show. And together, well, we're going to see what sort of uncharted territory it takes us to.
0:27Michael Stevens:And we want to hear your questions, your theories, your thought experiments. So send them in and stay tuned to see where we end up.
0:34Hannah Fry:Yeah, absolutely. And later on, I mean, there's not many spaces on the internet where I could use this as a hook and tease. But I think the rest of science is one because, Michael, later on I'm going to be showing you the coolest thermal insulator that I own. Okay?
0:49Michael Stevens:The coolest? Like, is it skateboard and wear sunglasses? and I'm trying to think of another cool thing. I don't know.
0:58Hannah Fry:Neither of us know cool things, let's be honest.
1:01Michael Stevens:Does it have ripped jeans and a bad attitude?
1:04Hannah Fry:Hey, maybe. You'll just have to tune in to find out. Or tune in, stay tuned, I guess.
1:16Michael Stevens:This episode is brought to you by Cancer Research UK.
1:19Hannah Fry:The word cancer comes from the Greek karkonos, meaning crab. And Hippocrates used that word because tumours can spread out like crabs legs.
1:29Michael Stevens:For a long time, cancer was poorly understood. And so I think because of that, it was almost scarier and people didn't even say its name. But what science has done since is replace uncertainty with understanding.
1:41Hannah Fry:But that understanding is an instant because cancer isn't just one disease. It's hundreds of different diseases, each behaving differently depending on where it is and its genes. And that complexity is why progress in cancer research can feel like it's slow. But step by step, research is saving and improving lives.
2:01Michael Stevens:And that's why Cancer Research UK, the world's largest charitable funder of cancer research, supports work across more than 200 types of cancer, from the tiny changes inside cells that start the disease to better ways to spot it earlier and treat it more precisely.
2:17Hannah Fry:For more information about Cancer Research UK, their research and breakthroughs, and how you can support them, visit cancerresearchuk.org.
2:48Hannah Fry:in Großbritannien und der EU.
2:56Michael Stevens:All right. Well, look, our first discovery doesn't even come from Hannah or me. It comes from you.
3:01Hannah Fry:It certainly does, because Hannah has sent us in a question. This one's for you, Michael. What was one landmark experiment you wish you'd been at?
3:10Michael Stevens:Oh, OK. I thought of a lot of experiments when I heard this question. I think that ultimately there are a lot of results I would have loved to have witnessed, but I'm going to have to say I would like to have been present at the Little Albert experiments.
3:31Hannah Fry:Ooh, these are some of the most controversial experiments in the history of science.
3:35Michael Stevens:Exactly. And I wouldn't have wanted to be there to be a part of it or to watch it happen. I would have just gone there to stop it.
3:44Hannah Fry:Oh, okay. We should probably tell people what they are for those that haven't. Yeah.
3:47Michael Stevens:So the little Albert experiments were done sort of early, mid-early 20th century. The results were published in 1920. The experiments were conducted at John Hopkins by John Watson and his grad student, Rosalie Rayner. The goal of the experiment was to see if they could teach a new fear to an emotionally stable child. Like already, it sounds like, let's just assume you can and not try. But they both did this. Rosalie is the woman that you see in the videos. If you really want to have a bad time, go to Wikipedia. Look up the little Albert experiment and you can watch the videos and she's the one there with the child.
4:32Michael Stevens:It's horrible. The research was based on Ivan Pavlov's work with dogs. OK, and and I don't know, I'll go on and on about this because I love psychology. But the point is, we've heard of the Pavlovian reactions. What that is about is called classical conditioning. Can I entrain a behavioral response to a originally neutral stimulus? And what that means in the case of the most famous experiment Pavlov did was when dogs are fed, when they smell food, they salivate at the mouth. So what he did is he rang a bell every time he fed his dogs. And when I say his dogs, I mean dogs in a laboratory. And he did this for many days until eventually he could just ring the bell and the dogs would start salivating even if he didn't feed them.
5:18Michael Stevens:And he's like, wow, look at this. So this is a huge part of what became behavioralism. The study of human behavior as essentially inputs and outputs. Like we learn things and we can be programmed like a machine. We've got buttons and levers and a human is kind of just like a steam engine.
5:37Hannah Fry:There's no evolutionary reason why it should provoke that involuntary response.
5:41Michael Stevens:Exactly. And so going off of this ringing bell associated with food, we start to combine them and we salivate when we hear a bell. Suddenly that might explain why we're afraid of things, why we love each other, why we decide to do the things we do, why we're greedy, why we're kind. All of this became less popular starting in the 50s. The cognitive revolution changed. And now, even today, we focus more on how we think, because ultimately, we know too much based on how many inputs we've received. Point is, let's get back to the experiment. Here's what they did. They somehow, they being Watson and Rainer, they found a nine-month-old child.
6:22Michael Stevens:We don't know how. We don't know the actual identity of the child. But in the paper, they called the child Little Albert. It wasn't its real name.
6:32Hannah Fry:Was Albert adopted or were his parents involved in the experiment too? Do we know that?
6:38Michael Stevens:We don't know. But all of the theories are that the mother was in the picture and aware of what was going on. The extent to which she really had a choice is unclear. She may have worked at the hospital and sort of felt like, I can't really say no because these people are like, you know, they have power over me in the hierarchy of John Hopkins research or they're my boss, you know, or we don't know. There are some guesses as to who the person might have been. The person, the baby, little Albert, may have been. I think the most popular theory is that it It was this individual who died at the age of six of a condition of the brain unrelated to the experiment.
7:21Michael Stevens:But that throws into question the validity of the results because this infant wasn't a completely healthy infant. Anyway, what did they do? OK, so they took this child and they presented it with all kinds of different objects. Literally, you name it. They showed it to the baby and the baby wasn't scared of any of it. The baby was curious. And then they decided, okay, let's associate something scary with one of these. And the one they chose was a white lab rat. They allowed the child to play with this lab rat. But every time they introduced the rat, the white rat, they hit a steel bar behind the child with a hammer.
8:01Michael Stevens:Boom, really loud. And the child started crying and needed to be consoled and was frightened. And then they would present the child with a rubber duck or a shoe. and they wouldn't hit the steel. Only when the white rat was there would the child be frightened. And sure enough, they were able to teach the child, little Albert, to be afraid of fuzzy white cute things. They could present the child with a rabbit and it would get scared. They were even able to present the child with a Santa Claus mask that had a cotton ball beard and the child would freak out and cry and scream. And they were like, wow, great job, everybody.
8:42Michael Stevens:We've learned that the human body is a machine that can be programmed and can learn. And like, that's just every behavior we have is some kind of learned thing. Now, despite just being like unethical by today's standards, it also didn't give us any good results. Like literally it was one subject with no control subjects and they didn't do follow-ups. They didn't then see if they could unlearn the fear from the child. They were just like, excellent that was cool um and it's very sad this is really the reason why this is considered such a
9:15Hannah Fry:sort of bad experiment in the history of science of course there were i mean look worse things have happened to people on earth right than them being than them being jump scared but the key point about this was that they spent days after days after days deliberately frightening a child right which is just already quite a horrible image um but they introduced this irrational fear in a human that they never undid, that they had no understanding of how that might go on to impact his life going forwards. And exactly as you describe, we didn't actually gain any serious or interesting scientific knowledge from.
9:53Michael Stevens:Yeah, it was not a scientific method experiment. It was a let's poke around and see what happens. Let's poke it and see if it bleeds and then we'll move on and go catch a movie. I want to say the only sort of silver lining is going to come from that thought of like sometimes out of trauma, growth can occur. Or at least like sometimes it takes despair for there to be triumph. And Watson, after these experiments, did a lot of weekend lectures. And he did one. And in the audience was a woman named Mary Cover Jones. and she was very interested in fear as something that could be learned. And so, of course, she thinks the kind of more kinder thought, which is, well, fine, but we should also maybe focus on how fears can be unlearned.
10:48Michael Stevens:And she happened to know a child that had been brought to her because the child was afraid of fuzzy white things. Strangely, it was not little Albert. This was like, I think, a six-year-old. So she says, well, I'm going to do the opposite of little Albert. I'm going to teach a child to not be afraid of furry white things. And she developed a method that involved something that I think a lot of us are familiar with today. Gradual exposure. All right. So just slowly introducing fuzzy things to the child and also having the child hang out with other children who were not afraid of furry things. and she was able to essentially cure the child of this irrational fear that was making the kid's life worse.
11:36Michael Stevens:And to this day, she's considered the mother of behavioral therapy. And so, I don't know, maybe little Albert's sacrifice brought us more quickly to behavioral therapy that helped people's lives. That's the only silver lining I can find in it. But I still think I'd go back and stop it because if it wasn't Mary Cover Jones, it would be someone else.
11:58Hannah Fry:Yeah. I mean, I think science was on that path, right? Of like learned behaviors. Sort of feels like it's only the adjacent possible to that is unlearning behaviors. Great answer though. Yeah. Great answer. I haven't thought about little Albert for a while. I'm not going on the Wikipedia to watch the videos. I remember watching them and finding them. I think maybe I was pregnant at the time or had a very small baby when I first watched them.
12:18Michael Stevens:Oh yeah. Terrible time to do it. I saw them in high school in a psychology class and I was like, what the heck um let's let's make adults scared of things i did that in a minefield episode i got electrically shocked every time a purple square was shown on a screen oh yeah and it did the same thing like like just uh it created an involuntary uh panic reaction whenever i saw purple squares
12:41Hannah Fry:but i consented to it has it subsided over time can you see can you see purple squares now yeah yeah it it evaporated very quickly how pink squares no no look away michael
Read the full transcript
12:54Michael Stevens:No, I'm fine. I'm not a nine-month-old baby. So I knew what I was saying, and I was prepared to accept a fear of purple squares for life.
13:03Hannah Fry:So, you know, I knew what I was getting into.
13:06Michael Stevens:Let's get into something else, though. Here's a question from Dr. Sonny Macon. If superhero powers obeyed basic physics and conservation of energy, which powers are actually the most expensive in energy terms? I'm thinking of things like super strength, flight, and super speed.
13:22Hannah Fry:Okay, you better believe I got out my calculator, Michael. Great. I've run some numbers, baby. Okay. Right, super strength. I mean, this is incredibly cheap. There's almost no energy involved in this. So let's say you're trying to lift up a tank, okay? Tank about 60 tonnes, all right? The work done, right? I'm going back to A-level physics here. Good. Mass times gravity times height, okay? know um that comes out about uh 1.2 million joules which sounds like a lot but in dietary terms it's um it's about 280 calories you're talking you're talking one snickers bar essentially half a milkshake easy peasy you can you can do that it's no big deal like one can of full sugar soda yeah i mean first of all i want to take a break that's like how efficient the human body is right
14:14Michael Stevens:That's like, oh, you know, you drank one can of soda. You better go lift. What was this that we're lifting? A tank. A tank. Go lift a tank and then you can earn yourself another. I don't want to say earn. Basically, let me just leave it at that. The human body is really efficient.
14:32Hannah Fry:Well, it's also it's also the wrong way to think about it. Like, you know, if you go on a treadmill and you're counting calories on your treadmill and you finish and you've like exhausted yourself and it's like 60 calories, you can have half a peanut. Yes. That's not the exact, it's extremely, extremely depressing. But the key point is that just being alive, just breathing, just being upright, just existing and thinking uses up a lot of calories. So you shouldn't ever think of calories as a sort of an equation in terms of your physical accession. But I'm doing it purely for the purposes of this question.
15:07Hannah Fry:And super strength is very cheap and easy okay flight i'm going to go medium level for flight okay okay um so if you are i'm going to just you know ignore the aerodynamics and just you know and just think of you pushing against gravity keeping yourself up that essentially means that you need to be a very a human inefficient helicopter okay um so you're if you're going to hover you've got to accelerate air downwards um and for human size objects i i work that out to be about let's say 100 kilowatts of power well that's quite a lot actually that is quite a lot you're gonna have to to eat please check my calculations by the way on this you can you can write to me tell me i've got it wrong but i think that's about 300 burgers per hour um which is quite a lot actually you've got you've got to you've got to pump through quite a lot um there i'm not because i'm not using aerodynamics if you were going forwards if you were gliding it would be more efficient but i'm just saying if you can just move yourself upwards like a like a rubbish helicopter um so that's kind of medium but uh by a long way the thing that is going to bankrupt you energy wise is super speed really speed is uh super speed is off the scale so um because for starters you've got kinetic energy kinetic energy by the way is the equation for it is half mv squared notice that v squared so the faster you get if you run twice as fast you need four times the amount of energy so super speed is it's going to scale very very quickly if you run at one percent of the speed of light which is
16:47Michael Stevens:compared to like a cosmic ray for example it's nothing snail's pace it's not moving yeah you've
16:54Hannah Fry:also got air resistance here that you've got to consider.
16:56Michael Stevens:I was wondering if you were going to factor that in. Yeah.
16:59Hannah Fry:Here it is. Here it is. Air resistance scales with V cubed, my friend. It's the cube law. Oh, lordy. So if you're going to run twice as fast through air, you need eight times the power to push the air out of the way. So, you know, let's make it slower. Let's just say you're running at the speed of sound. You're not just burning calories. You're generating heat from air compression, you know, that's enough to melt lead. And, you know, if you're trying to run at the speed of light, which I think is what Superman does, you know, I've seen the videos of him circulating the earth. I don't think it was a documentary, but yeah, I mean, you're going to be causing nuclear explosions all over the place.
17:48Hannah Fry:Obviously, every time I do one of these calculations, it ends in nuclear explosions.
17:52Michael Stevens:As it should, as it should. So super speed. I mean, yeah, listening to you explain it, it makes sense. Super speed also requires super strength because you're having to push an enormous amount of air out of the way very quickly.
18:07Hannah Fry:Yeah, you really are.
18:09Michael Stevens:All right. So we went from a Snickers bar to 300 hamburgers an hour to constant nuclear bomb explosions.
18:19Hannah Fry:Exactly. It's a simple, simple scale, simple linear hop, skip and a jump from one to the other. Okay. All right. Here's another question. Oh, okay. This is nice. This is from Owen, who wants to know when we first met, Michael.
18:32Michael Stevens:Oh, yeah. I remember. Do you remember? I think I remember. I think we've talked about this before. I mean, I was aware of you because of your appearances on Numberphile. Correct. I don't know how we got in touch, but we went to lunch. Why did we do that, though? Like, did I have your email address?
18:56Hannah Fry:Let's think about what year this was. This was probably, what do you reckon, 2014, maybe?
19:00Michael Stevens:That year would have been 2015.
19:03Hannah Fry:2015, there you go. You were working at YouTube in London.
19:06Michael Stevens:Yeah.
19:08Hannah Fry:And you had been running vSource for a few years by then already. so I had obviously watched every single one of your videos yeah of course um of course uh as most of the internet had and uh I was in YouTube recording a video and then as I was leaving you
19:26Michael Stevens:happened to be in the lift right that makes sense okay so we just ran into each other at the YouTube
19:32Hannah Fry:office in London yeah yeah you were very cool and I was not what do you mean cool I remember the entire conversation, Michael, you were like, I was like, oh my God, it's be awesome. And didn't want to say anything. It stood in the corner. And then you were like, oh, hang on, you're Hannah. And I was like, oh my God.
19:54Michael Stevens:No kidding. I had really, I was really nervous because you were like an actual smart person. I was just a guy who was like, look at this cool thing.
20:03Hannah Fry:And then I was like, oh my God, you know who I am? And you were like, well, yeah, it's kind of my job to know. I work for YouTube, right? It's the kind of fun job to know. And then you said that you were working on a video for Banak Tarski and you needed a proper mathematician. And I didn't know any of those.
20:19Michael Stevens:We had lunch and you were gracious enough to listen to me basically do the Banak Tarski video live. Which was great. And I just needed someone to tell me, does this make sense? Can it be followed? Are there any egregious mistakes and your interest in it. And also the fact that you weren't immediately like, okay, no, this is obviously wrong. Gave me so much confidence that I made the video. And if you look at the history of Vsauce, that's a turning point in the channel where I went from, oh, could you eat your own poop if you cooked it first to I'm going to take a long time to really dive into something to explain something that I can't understand that hasn't been taught, I think, just in the right way yet.
21:11Michael Stevens:And I'm not going to do it right either, but I'll at least add a different voice to it. And so every video after that is like more than 20 minutes long. Every video before that one is like eight minutes long. So yeah, you played this like pivotal role in the evolution of the channel and myself. So that's how we met.
21:32Hannah Fry:The Bannock-Tarski video, by the way, I should tell everybody, is talking about an extremely obscure and mind-bending mathematical theorem where when you take the surface of a sphere and rearrange it in a particular way, you can end up with two of the original object without adding or deleting anything. It's extremely mind-bending. And I think up until that point, really nobody had delved into anything that complicated in a public forum, in a sort of, in a, something that was to be consumed by everybody. And those of you who haven't seen Michael's video on Banachowski, I think it's got something like tens and tens of millions of views, right?
22:16Hannah Fry:Yeah, something like that. It is wild to the entire mathematical world that you could take something that mind-bendy and bring it to totes to so many people.
22:26Michael Stevens:I know, there's an appetite for it online. And I think ever since then, not that I started it, but I knew these things would be popular. And now, thankfully, we've got Three Blue, One Brown. We've got all these channels that are like, no, let's do it. Let's get into this. And now it's like, no matter how deep of a question I have, I'm like, what exactly is energy? or why did chimneys break in the middle when they fall? There's always some like Indian YouTuber who's like, let's get into it. And they draw out every single thing and what each formula means. And it's just, it makes me feel so great for the human race that we want this kind of content.
23:10Michael Stevens:So yeah, with Bonnettarski, there's like one thing I wish I had done differently, which is the way I describe choosing the first set of points from the sphere. I could have been more clear about. So one of these days I'll revisit it. But yeah, the point is that this very paradoxical dissection puzzle requires removing points in very precise ways and then putting them back together and like, oh crap, I have two now. Wait, where did all this extra stuff come from?
23:40Hannah Fry:But that's how we met. There you go. Oh, that was a really nice, that was a really lovely question. Thank you. Yeah, thank you very much, Owen. Should we take ourselves to a break after that? Yeah.
24:05Michael Stevens:This episode is brought to you by Cancer Research UK.
24:09Hannah Fry:Radiotherapy is over a century old, but it is still changing. Cancer Research UK helped lay the foundations of radiotherapy in the early 20th century and has driven progress ever since.
24:21Michael Stevens:Radiotherapy remains one of the cornerstones of cancer treatment today. Every year, millions of people worldwide benefit from Cancer Research UK's work to make it more precise.
24:31Hannah Fry:Scientists are still refining how radiotherapy is delivered. And one example is an experimental treatment called flash radiotherapy, which delivers radiation in fractions of a second, up to a thousand times faster than standard radiotherapy.
24:46Michael Stevens:And early studies suggest that speed could make a real difference. Flash radiotherapy may cause up to 50 % less damage to healthy cells.
24:55Hannah Fry:But scientists don't yet know why healthy cells seem to be spared, so Cancer Research UK are working to answer that. Understanding it could be key to reducing side effects in the future.
25:07Michael Stevens:For more information about Cancer Research UK, their research and breakthroughs, and how you can support them, visit cancerresearchuk.org forward slash the rest is science.
25:24Hannah Fry:This episode is brought to you by Thriver. Most of us tend to think of blood as something slightly clinical, linked to illness or bad news. But in reality, it has been quietly keeping a record of what's going on inside our bodies. Almost like a biological diary.
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26:59Michael Stevens:Ausprobieren.
27:08Hannah Fry:Welcome back, everybody. I promised you some thermal insulation and I'm going to deliver. Oh, I'm going to deliver on the most exciting thermal insulation that there is. Not just in the world, but I'm going to say in the solar system. Okay, that's where I'm going with this, because I'm talking space here. I want to bring you back, Michael, to the 1950s. when the space race was in full force and there was an incredibly difficult problem that people were trying to solve, which is how on earth do you get vehicles from space back to earth? The re-entry vehicles for NASA. Now, the thing is, is that getting rockets out of the atmosphere, actually that bit's kind of easy.
27:51Hannah Fry:I mean, maybe easy is a bit strong, but it's not too difficult. When you're coming back down, though, you are traveling at such an unimaginable speed that you have so much air that needs to get out of your way. You're squashing this air so rapidly with such a force that the temperatures that you start reaching are way higher than basically any human-made product could withstand. so so back in the 1950s there's a guy called harvey allen and he's set the task of um designing these these re-entry vehicles for nasa and the first ideas everyone was like well we just need it to be like a rocket shape basically we need to um make it as streamlined as possible like slice through the air yeah like a needle right pierce through it get through the atmosphere quickly minimize the drag minimize the friction forces on the side get in um but these temperatures as these speeds i mean they are so massive that it's just it just wasn't nothing would work so harvey had this absolutely genius idea because he realized that when something is streamlined um all of that heat it's going to happen right next to the skin of the vehicle right it's like literally on the surface and really what you want you want some kind of a like a buffer like a protective blanket that you can sort of wrap around the re-entry vehicle and take some of that heat away.
29:25Hannah Fry:So his idea was, what if, what if instead of making it streamlined, you just deliberately make it as unstreamlined as possible, right? What if we make the aerospace equivalent of a manhole cover, right? That's essentially what he was thinking. And the point about this is that if you re-enter the atmosphere with like a massive flat wall, then the air that's getting crushed it can't get out of the way quick enough so it ends up forming this um this basically a cushion at the front of the vehicle you get a much bigger shock wave um you get way more friction but it happens away from from the skin of the vehicle so that then it's not in direct contact with the sort of human-made substances around the side but it's kind of directed around it I love this idea.
30:15Hannah Fry:I love this idea of backwards thinking. And this is exactly what they ended up doing. So even, I mean, they started off with these sort of these round shapes. The Russians copied the ideas. They used spheres. The Americans sort of settled on that cone shape, which would come in, it's sort of belly flopping into the atmosphere. And then even the space shuttle, which looks more like a plane, right? But when it would come into the atmosphere, it wouldn't go nose first and dive through. It barely flops, right? It kind of comes in. So this was the general idea. But still, even still, the temperatures on the surface could still get up to 1 ,250 degrees centigrade.
31:01Hannah Fry:grade, but it's still vast, vastly higher than anything that would be, you know, you can't have like a metal skin on the outside, for example.
31:11Michael Stevens:Because it would melt.
31:12Hannah Fry:Because it would melt. Exactly. So I should tell you, actually, I did a video on this. I did a little social media video about this. Just I really love the aerodynamics of re-entry vehicles. I just think there's something deeply amusing to me about there being such a difficult problem and people turning it upside down and going for the most un-aerodynamic space possible. So I did this video about it. And then I was in California and I was in Google actually. And someone came up to me and they were like, oh, I knew you were going to be here today. I just finished working for NASA. Now I work for Google.
31:52Hannah Fry:and I have for you a tile of the particular material that was used on the space shuttle. This is the material that they came up with that was the workaround for these absolutely insane temperatures on the space shuttle.
32:12Michael Stevens:Yeah, we're looking at a tile of, it looks like white foam. It's about the size of a domino or maybe two dominoes on top of each other. stacked hamburger style. But it's also striated on the sides like a cake made of very thin layers all stacked up with black and white lines. It's a glossy black paint on one face, one of the large faces, but then it's white everywhere else except for those thin black lines on the sides. And on the back, though, it looks like it's made almost differently of transversely organized sections.
32:50Hannah Fry:basically what you have is these many many many layers both horizontally and vertically um and this is actually it's pure silica it's 100 silica huh um but it's these fibers that are laid in such a way that this block is 94 air okay so it's it messes with your mind because you look at it it sort of looks like um i don't know like a piece of chalk perhaps it's sort of white and it's got almost powdery. Yeah, I was going to say like ceramic or chalk. Yeah. But when you pick it up, it's way lighter than your brain thinks it's going to be. It's unbelievably light. It's essentially solid air. That's what they've created.
33:34Hannah Fry:Solid air. Solid air. I love that. Trapped in a cage of silica. It was invented by Lockheed Missiles and Space Company. This one specifically for the space shuttle. it's called li 900 uh the the 900 in it stands for its density it's nine pounds per cubic foot okay so there you go americans this is uh you can tell this is made in america yeah but for context by the way styrofoam is three pounds per cubic foot so this is slightly heavier than styrofoam but but not by much it's sort of that that's the sort of weight that it is the thing about this stuff is that it is because it is you know sort of solid air in a lot of ways um you could easily crush this you could like just put your hand through it I mean it sort of feels quite fragile under um under your fingers now the thing is all of these little pockets of air in here air is this It's unbelievably good insulator.
34:39Hannah Fry:You know, heat doesn't really like traveling across air gaps. So when you have, you know, an unimaginable number of tiny little caged air bubbles inside a material like this, it means that it is so poor at conducting heat that you can literally put this in a kiln, heat it to well over, you know, a thousand degrees centigrade, 2000 degrees Fahrenheit.
35:03Michael Stevens:So it's glowing hot.
35:04Hannah Fry:It's glowing hot, literally red hot. And yet you can still pick it up with your bare hands because it is so bad at conducting heat that it's not going to burn your skin. It's wild. It's wild. There's this video of people doing that.
35:22Michael Stevens:I've seen the video, but I never really knew what they were made of. But now hearing your description of these silica fibers makes me think that it's almost like a possibly safer version of asbestos because both of them are like woven rock fibers made into a material um they're both bad to get in your lungs but i don't know that silica stuff might be a little bit less carcinogenic only one way to find out though hey come back in five years let's see so let's probably put it back
35:55Hannah Fry:in a little box shall i um i didn't know that's how asbestos work is it asbestos like trapping loads of um just traps loads of air molecules in it does it yeah it's like uh it's also like it's
36:07Michael Stevens:rock so it's it's it's flame proof fire resistant and it traps in air and uh so it insulates really well um it yeah it doesn't burn um it's really marvelous stuff except for that one problem
36:23Hannah Fry:that one tiny thing there was asbestos in my house actually when we um when we did up my house there was asbestos everywhere. And I got really scared because I'd had my babies in this house, sort of sleeping next to asbestos walls. And they said that actually, until you disturb it, it's completely fine.
36:41Michael Stevens:It's fine. It's a rock. It's sitting there. But once you decide to like remove it, that's when you've got to do a lot of safe precautions because it breaks into little tiny, little tiny like needles that float in the air and you breathe them in. They get stuck in your lungs. They don't dissolve or digest or anything because it's rock. And for reasons I'm not really clear of, it also accelerates cancer. It's not just like it clogs up your lungs. So yeah. What is the disease called? Mesothelioma?
37:15Hannah Fry:Something like that. We should talk to our friends at Cancer Research UK. We should.
37:18Michael Stevens:Yes. Yes.
37:20Hannah Fry:So here's the thing. OK, so this idea of LI-900, they knew that they'd solved it, that they'd found something that was just an unbelievably good thermal insulator. But these tiles are so incredibly fragile. You can't have them as big. They can't be large. They couldn't just create these massive tiles, put them in and off you go. The space shuttle wasn't covered in this uniform blanket. It was covered in 2 ,400 tiny individual tiles.
37:53Michael Stevens:Oh, wow.
37:53Hannah Fry:And because the space shuttles bend and flexed during flight, you can't just glue all of these tiles directly to the metal skin underneath because they would snap. There was this strain isolation pad, which was then glued to the ship. and then every single tile on top had a unique shape, right? Which means if you broke one of them, you can just go and grab one off the shelf.
38:20Michael Stevens:You've got to grab that shape.
38:22Hannah Fry:That exact shape, that custom replacement for that specific coordinate. These were an engineering nightmare, these things, because the other issue is that, you know, these are 94 % empty space, right? Like they're solid air, as it were, which means it's incredibly porous. So if it's raining while the shuttle's sitting on the launch pad, the tiles would absorb like hundreds of kilos of water. Right.
38:49Michael Stevens:They would become solid liquid water.
38:52Hannah Fry:Solid liquid water. Exactly. And then you've got problems. Maybe that water could freeze. It could expand. It would shatter all the tiles. It would boil off in orbit. It would blow them all apart.
39:04Michael Stevens:A lot of extra weight suddenly you've got to launch. Yeah. Right.
39:08Hannah Fry:So then they're having to like inject these tiles with this waterproofing agent. Basically, you know, Scotchgard on steroids, essentially, via a needle. They've got to do it in all of these gaps and all of these holes. But one of the ways around this to sort of seal the outside is, especially on the belly, is they have this glaze that they put on it, this reaction cured glass, this borosilicate. and that helps to seal it but also maximizes the heat immiscibility, sort of sheds heat back into space. So these are on the bottom and then the white tiles, these are the ones on the top.
39:47Michael Stevens:Cool, huh? Isn't that cool? Yeah, because the bottom of the space shuttle is black. And so I was wondering, so is that what I'm looking at there? Yeah, the black side is the side that faces out during the belly flop.
39:59Hannah Fry:Yeah. Isn't that amazing though? So like this complete paradoxical material, something that's like fragile enough to be crushed by a toddler, but strong enough to survive this plunge through the atmosphere at like over a thousand degrees.
40:14Michael Stevens:Yeah, I think that describes a lot of people I know. I love it too, because we talk so much about to leave Earth, how hard it is to leave, to have the delta V required to leave our cradle. And yet coming back home is its own engineering problem. It's like the Earth doesn't want to accept us back readily.
40:38Hannah Fry:I always thought that was the hardest bit. The whole thing about whether the moon landing was real or not. I always thought that the argument for me was that getting to the moon and landing on the moon actually might be difficult, but not anywhere near as difficult as the problem of getting back off the moon, getting back down to Earth and landing safely. And that was always the thing is that you had this moment in time, these, well, unbelievable geopolitical pressure for this, for the space race, combined with, you know, launching missiles and nuclear weapons from space and all of the sort of defence side of things that came with that.
41:18Hannah Fry:but you also had incredibly gung-ho pilots. I don't think it would have been difficult to find somebody who was willing to do a suicide mission to the moon and just stay there. Like that bit wasn't hard. So it always seemed to me that the showy bit wasn't the hard bit, which makes me believe that they did the entire thing.
41:38Michael Stevens:Have you seen that video where the guy shows that in 1969, it would have been easier to have gone to the moon and come back than it would have been to create a broadcast of that length, like a pre-recorded film segment. Yeah. He's like, actually, that feed of the moon landing is so long that if you had done it in a studio beforehand on film and then you had to play it back like it was live and not have a single piece of dust or a hair on it, not allow any mistake to show that you're just playing back a reel, Like that would have been an even bigger technological miracle than actually going to the moon and back.
42:18Michael Stevens:It's a very fascinating video.
42:22Hannah Fry:Yeah, I think, you know, I sort of vaguely do remember he was talking about the size of the reels, like the physical size of the reel of tape, right, if I remember rightly.
42:30Michael Stevens:Yeah, because he's talking about like hours and hours of footage that is like streamed out onto televisions. And somehow it needs to never look that way. It needs to look like a live broadcast. So it probably was because if they had solved that, that would have been more unbelievable and more of an achievement than the moon landing. The other argument that I find compelling is that how many thousands of people were involved, right?
43:01Hannah Fry:How many, the cleaners, the sort of the janitors, the like people who are painting the walls, all the way through to the engineers and the astronauts and the people in politics. Not one of them, you know, not one of them, however many decades later, slipped up and accidentally told everyone that it was a ruse. I mean, I just don't believe in humans that much. I just don't believe in humans' abilities to keep secrets that much.
43:27Michael Stevens:Yeah. Oh, yeah.
43:28Hannah Fry:Okay, well, we're hearing from our producer that LI900 would need exposure to 1 ,450 degrees centigrade for hours, then crushed to have any carcinogenic potential whatsoever. So, live to fight another day, Michael. Wow, you're safe. Okay. Important that you recognize I was willing to put my life into your hands for the purposes of this podcast. I know. I know.
43:53Michael Stevens:But now we know that you were safe all along. So I feel better. All along.
43:56Hannah Fry:All right. Well, I guess we'll leave it there for this week. As ever, if you have any questions, ideas, tiles off the space shuttle that you want to send us, you can email us, therestisscience at goldhanger.com.
44:10Michael Stevens:And you can join our newsletter at therestis.com slash science.
44:16Hannah Fry:We're going to be back next Thursday with another edition of Field Notes and on Tuesday with our normal episode.
44:21Michael Stevens:So until then, stay curious.
From the publisher
Rockets are built to slice cleanly through the atmosphere on the way up. Coming home, it turns out, requires... not turning into a fireball before a bellyflop
When Space Shuttles reenter Earth’s atmosphere at 17,000 miles per hour, they don’t dive nose first. Instead they turn broadside to the atmosphere, deliberately creating more drag, more friction, more heat. At those speeds, oncoming air compresses into a shockwave hotter than molten lava.
In this episode of Field Notes, Professor Hannah Fry and Michael Stevens explore the strange physics of coming home. Why is leaving Earth easier than returning to it? And what does a small, almost empty black tile reveal about the problem of meeting the world at 17,000 miles per hour?
Along the way, they revisit controversial experiments in human fear, calculate which superhero power would bankrupt you in calories, and reflect on the thin boundary between surface and survival.
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For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit https://cancerresearchuk.org/restisscience
Cancer Research UK is a registered charity in England and Wales (1089464), Scotland (SC041666), the Isle of Man (1103) and Jersey (247). A company limited by guarantee. Registered company in England and Wales (4325234) and the Isle of Man (5713F). Registered address: 2 Redman Place, London, E20 1JQ.
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