The Rest Is Science - Why Your Body Needs Gravity

Episode Date: September 13, 2026

Does space travel make astronauts younger? Professor Hannah Fry and Michael Stevens explore Einstein’s twin paradox, time dilation and NASA’s famous Twins Study with astronauts Scott and Mark Kelly. After Scott Kelly spent 340 days aboard the International Space Station, he returned milliseconds younger than his identical twin. But microgravity had also affected his eyesight, bones, blood, gut microbiome, body temperature, genes and telomeres. So what exactly happens to the human body in space, and which changes remain after astronauts return to Earth? In this episode, Hannah and Michael discover how deeply the human body depends on gravity. Along the way, they uncover why your head ages faster than your feet, what a 63 day cave experiment reveals about our sense of time, and whether future humans could ever truly adapt to life beyond Earth. ------------------- For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit ⁠https://www.cancerresearchuk.org/our-research/rest-is-science 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. ------------------- Find The Rest Is Science all over the internet by ⁠⁠clicking here.⁠⁠ ------------------- Video Producer: Teo Ayodeji-Ansell  Animator: Sam Benson Video & Social: Bex Tyrrell Assistant Producer: Lucy Lipscombe Producer: Simona Rata Senior Producer: Lauren Armstrong-Carter Chief Digital Officer: Samuel Oakley Exec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

Welcome to the rest of science. I'm Hannah Frye. And her hair is ginger. Yes, it is. I haven't mentioned it. It doesn't really come up. I hadn't noticed, honestly, I'm very colorblind, you know, in that way. We're all people. What if you were colorblind? And you just, I mean, colorblind, like, I just don't even know. You're just a human to me. Just another human.

Anyway, my name's Michael Stevens. And this is the rest is science. Okay, Michael. For today's episode, I want to tell you a story about two men. they had the same face they were twins not that much of a mystery one of them gets onto a rocket ship in Kazakhstan

the other one drives home to Arizona now I know what you're thinking Einstein talked about this he said take two twins put one in the rocket ship send them away from the earth they'll come back

there'll be different ages I want to talk to you Michael today about what actually happened when people actually tried it for real. This episode is brought to you by Cancer Research UK. As if they weren't cool enough already, some astronauts have now added cancer scientists to their CV. They are making use of microgravity conditions in space

to carry out experiments. That's because the same thing that lets astronauts experience weightlessness also affects how cancer cells grow, behave and respond to drugs. And back down on Earth, Cancer Research UK is working with astronomers to explore tumours with technologies that are typically used to map the Milky Way, which I think gives you an idea of just how complex this disease is.

That's right. There are over 200 different types of cancer. But by pushing boundaries and embracing the latest technologies, Cancer Research UK has helped double cancer survival in the UK over the past 50 years. And today it is continuing to save and improve lives around the world. For more information about Cancer Research UK, their research and breakthroughs, and how you can support them. Visit cancer researchuk.org. Trade ice skating at Nathan Phillips Square for ice cubes in your umbrella drink. Let Porter Airlines fly you from Toronto Pearson nonstop to 10 top sun destinations in Mexico, the Caribbean and Costa Rica.

Enjoy award-winning Porter service Toronto has love for 20 years and start your vacation as soon as you're on the plane. Book your sunny getaway today at flyporter.com and actually enjoy a comedy. You gotta try breakfast, I gotta try bread. And what better way than with a delicious Pratt organic coffee, starting with just $1 all day, every day now until December 31st. You gotta try breakfast at A&W. At participating A&W locations in Ontario. This is a real story. Oh, I'm making up. You're talking about the bald twins.

Huh? Are they bald? Do you know what? I actually know what they're like. I'm pretty sure they are. I know every bald man. They are bald. Aren't they lovely men?

I can't remember their names. Kelly? Yeah, Scott. Yeah. One of them is like a senator. Oh my God. That's Mark Kelly. Yeah.

Yeah. I cannot believe I've been researching this for like two. days and I didn't put two and two together. Wait, were they both astronauts or just one of them? They were both astronauts. Okay. Mark was a retired astronaut. Mark has done a wonderful job of literally finding a way to be known for something besides the fact that you're an astronaut. Right. He comes up in the news all the time and I'm like, he's an astronaut. I can't even mention that at this point. Can you imagine having a life like that where you're like, oh yeah, I've been to space.

But that's not even what they say about me most of the time. It's not even the most interesting. thing about me. I know. Wild. I cannot believe I didn't put two and two together because I follow American politics all the time, like all the time, know all about Mark Kelly, genuinely, was so interested in what happened in this experiment. It never even occurred to me to think that that name might ring a bell. Have you met any astronauts, by the way? Yeah, I have. Which one have you met? Don Pettit. Right. And I met him like twice. So technically, two, two, because he's made of different atoms the second time. I completely agree. You know, No man standing in a river is the same man.

Different river, different man, right? Yeah, different astronaut. Different you as well. It was a different me. Have I even met anyone? This collection of Adams has not. Here's the thing. I think astronauts, they're as close to a superhuman species as we have.

I think if you filtered off just the astronauts, it did an astronaut breeding program, you know, I think quite quickly they would divers. from the rest of us. They are so special, so smart. They're like the smartest people, incredibly fit, unbelievably brave, and also just really, really kind and decent. And there's a demeanor to them that I don't know if they always have that and they self-select for astronauthood or if they become that way as they become closer to astronauthood. I also wonder whether having to face your own mortality, which I think you have to do if you are going to do something that is really as, you know, I mean, you're taking your life and you're strapping yourself to what is essentially a bomb and blasting yourself out of the atmosphere of our planet.

But not for the thrill of it. The guys who do that with Red Bull are very different. An astronaut has this sort of humility, this kind of service-oriented personality. I'm here to serve this agency, the American people or the people of my country. It's very, it's very cool. It's really, really, really cool. And I think that this experiment of Scott and Mark Kelly demonstrates just how willing they are to give themselves over in the pursuit of knowledge and science. for all of humanity, not for just themselves. And astronauts are not perfect, by the way.

Sure. I just want to say that, because you can read some of their biographies, and you'll be like, oh. But in terms of public persona, they are like a kind of person I've only met a few of in my life. Right. I find them so much more impressive than actors, than musicians. Than podcasters. Can you imagine looking up to us? I find them so much more impressive than basically anything else.

Athletes can be really impressive. The sort of single-minded pursuit of a goal, of an ambition, of like pushing the boundaries of what's humanly possible. And the natural talent to do what they do. And it's like, I will never do that. I will never win an Olympic gold medal. No, agree. I will also never go to the moon.

No. I mean, I might be able to, but I will choose not to. so that what I just said will stay true. I mean, frankly, absolutely the same. Okay, shall I tell you about this experiment? Yeah. Genuinely fascinating. All right, so let's kick off with what Einstein said about twins.

Okay. The twin paradox, is it no? Classic. So he proposed this as a thought experiment in 1905. And what he said is, okay, so you've got two twins born on the same day on Earth. You pop one on a spaceship, send them off on a journey 10 light years away from Earth. But they're traveling at, this wasn't Einstein's numbers, but let's say, Let's say 86.6% of the speed of life.

That was a specific person. It was specific, wasn't it? Yeah. Now, the reason why I chose that number is because at that speed... 88.6% the speed of light. 86.6.6.6. Got it. Okay. Yeah. Okay. I can see you're going to do the calculations in your head, Michael. No, I'm not. I just... I want to remember because there's a cool fact about it.

You're about to tell me. There is. I don't want to forget it. Okay, you ready? 86.6.6% speed of light is special because... It's special because it means that time... on Earth will travel faster than the speed on the spaceship by a factor of two. Double. Okay, perfect. All right.

So at that speed, I'm traveling at that speed, my stationary twin on Earth is going to be aging twice as fast. Correct. Right. So if you go off your pop, right, accelerate away, 10 light years away, turn around, come back, by the time you come back, it's going to have taken you 11 and a half years. They're twice as old as me now, even though we're. were born on the same day. And it took me 11 and a half years to go 10 light years?

Correct. But then I have to come back. Yeah. Why did it only take me 11.5 years? Shouldn't it take me 10 years to go at light speed? So in total, the distance that you've traveled is 20 light years. Okay, yeah, because you went 10 light years away and back. Correct.

However, you're going at 86.6% the speed of light. So that's where you get the 23 from. That's how long it took, according to your... twin on earth. Yeah. Your twin on earth is like, right, off you go. You distance and time. It's very simple. Speed is distance over time. I know your speed, 8.6.6.6% speed of light. I know the distance. 10 light years. I'll see you in 23 years. See you in 23 years. But for you who's traveling so quickly, how long has elapsed according to your watch? 11 and a half years. Just a just half as long. Half the time. Wow. And you come back and you're like looking in your twin's face and you're seeing your

future, essentially. You are seeing what lies ahead of you in your body. 11 and a half years from now. Exactly. You say, I will look like that. Right. Bummer. Bummer. And your old twin is like, oh, maybe great. Or maybe great. Probably great. Probably great. The way twins are, you know. Yeah. And your, your earthbound twin is looking at you going, oh, 11 and a half years ago, I had that appearance. So fresh-faced. More or less. I mean, things can happen. Maybe, maybe you, you know, decided to agree. a beard and your twin didn't. I don't know.

There could be some differences. It could be. But the point is... Maybe your twin on Earth really took up smoking and drinking heavily. Can I ask you another question? Go ahead. So, okay, you're on the ship.

And the whole trip, the 20 light year round trip, only took 11 and a half years for you. Yes. Is it confusing to be like, wait a second. I just traveled 10 light years from Earth. I wasn't even going at light speed 100%. Right. But I still, I got there in like,

what, five and three quarters of a year? If you asked a photon who just traveled a hundred light years, how long did that take, they'd be like it was instant. Yes. So it's fine. This must not be a problem. Yes, because the distance itself is effectively length contracted, isn't it? Oh, that's it.

Yeah. Like the photon, when it leaves a star and it lands in your eye a billion years later to the photon, your eye was right next to the sun. It just comes out into your eye. Hi. If it was conscious. That's what it experienced. Yeah, because this is the whole point about space time, right?

That space time is only according to your particular perspective. So that whole like speed is distance over time calculation only works when you're standing on earth and it's like, all right. It's a good approximation. Okay, not to be the Newton flag bearer guy, but like most of the time, I can go ahead and assume that the universe has depth. Yes. And it works. And it works. I'm able to seat my baskets.

Yeah. Because I'm really good at basketball. Yeah. It's just a humble bragging. can reach out for a handshake and expect the person's hand to be where you thought it would be. And it's not like, whoa, my hand moved so quickly. My hand is like so much younger than me now. Suddenly the distances and the time.

Anyway, right, here's the point about the Einstein thing is like, once you get up to really fast speeds, once you're traveling long distances, close to the speed of light, everything goes a bit woo-woo. Right. Everything goes a bit strange. All it's dilated. It's all problematic. Your twin on earth is older than you.

That's the key point I want you to remember here. It's bizarre. Okay. So NASA, being NASA, we're like, guys, we can sort of try this. Why don't we just give this a go? We've got Mark and Scott Kelly. Let's just pop one of them in a spaceship, see what happens. Tiny problem, small, is that, unfortunately, getting a spaceship up to towards the speed of light

and traveling 10 light years away, it's just beyond their capabilities. Right. An appreciable amount of the speed of light, not going to be. going to be reached anytime soon by any space agency. So they went for the next best thing, which is they put Scott on the ISS for a year almost. Okay. All right. And how fast does the ISS go as a percentage of the speed of light?

Okay. So it orbits as a, well, it orbits at about 7.66 kilometers a second. I mean, that's fast. That's fast. That's fast. That's not light speed fast. It's not light speed fast. it's about 0.00256% of the speedflight.

That's fewer knots than I expected. Yeah. Just 2?002. Wow. Okay. So, I mean, that's small, but I was expecting like 12 zeros. Right, okay. But the ISS is fast.

Look, 7 kilometers a second. You kidding me. That's super fast. You blink your eyes and you're... Traveled across London. Wow. Not quite. Half of London.

All right. I think you're eyes slowly. So NASA did this twin experiment in real life. They did. Here's the thing about it, rather than it being a factor of two, which is what it was in the example. I can give you, or the aging twice as fast as you. Instead, one twin will be aging 1.000000-3-275 times faster than the other. There's all the zeros I was expecting.

It's about 3.3 parts per 10 billion, basically. that's how much faster. Okay, say that again. Three parts per 10 billion? Yeah. Okay, so for every 10 billion seconds, yeah. Your twin on earth lives. You only live 9,99,997.

Exactly. That's exactly. That's still pretty cool. It's still pretty cool. Once you put it all in, once you do all your calculations, over 340 days, which is how long Scott Kelly was was in the ISS, for, in total, one twin is between five and eight milliseconds older than his brother. Five milliseconds? What can even happen in five milliseconds?

I mean, not much. Not much. If you want to pump it up there, you can. If you went up there for like three years. Right. If you wanted to get a second on your brother, you just need to do a simple 110 years in orbit. Ayah, y'i. We got to get those numbers up, NASA. You know what, they? You would come back and be like, like, wow, that's what I'm going to look like in, when I started this sentence. Yeah, right. My gosh. I'll tell you what, let's have a break and I'll do more when we come back.

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All right, we're back. So is this graph of like time dilation? It's not linear. Correct. So if you go half the speed of light, you're not halfway to not experiencing time at all. Correct. It's probably the graph's probably like that or something. Yeah, it's called the Lorentz factor.

The Lorentz factor. That graph is probably shaped where it's like, oh, if you're going 0.002% the speed of light, basically no change. But once you get up to like 80% or beyond, then it's just. like, whoa, now you're going to notice it. And then it flattens off as you go further on. Uh-huh. Yes, you're basically at one, your factor, you know, a factor of one, essentially, up until about half the speed of light, that's when it starts picking up.

Really? Once you get up to 0.8, 0.9, that's when you get like, that's when you're doubling, right? Right. So you're, you traveling that fast are aging half as quickly. Correct. As someone who's stationing. Correct. That's when your factor is too.

But, you know, you get really close to the speed. of light you can have 10, a factor of 10. I mean, you can have any number you like. You get super duper duper close. Yeah. You could be like 100 if you want. Right. I'm just, I'll just spend just a year up there.

And I come back and be like, oh no, everyone you love would be dead. They'd be dead. Yeah. Yeah, maybe don't do that. But that's the theory anyway. That's like Einstein's theory of how one would age compared to the other. But NASA aren't stupid, right? They sort of knew that they wouldn't be able to actually actually measure the different.

of five milliseconds of life. But what they did do, and the reason why they did this twin study, was to look at the impact of physically being in space. Ah. Not just because of general relativity. But all the other things. All of the other things. That have much bigger effects, like no G-force on your body for a year.

Right. Between the two brothers. Probably more radiation. Right. And let me tell you, Michael, the effects of being in space are mental. Right. Completely insane. All right, tell me, what happened.

Okay, so one of the big things, one of the astronauts I got to meet, he is not allowed to be in space anymore because being in space has changed the physical shape of his eye because of the way that the pressure changes. So on the ISS, they have to have loads of spare pairs of glasses up there floating around. Your prescription changes. Your prescription changes. Why do your eyeballs change? because surely the air pressure inside can be made similar to Earths.

Right. It's not just about pressure, though. I mean, so your optic nerve swells, you get all these folds that appear. You get, it's sort of like wet wallpaper, basically. Yes, because there wouldn't be gravity keeping the blood away from your eyes. Totally. It's like, I'm going to be here. So, I mean, the whole shape of it changes.

Yeah. And then permanently so in some cases. There are some astronauts. There's one guy called John Phillips who went up, had 20-20 vision when he went up. And then when he came back, it was 20 out of 100.

I don't know loads about how those numbers work, but I think that's not good. That means that what a person with normal vision can see from 100 feet away, he'd have to be 20 feet away to see. Okay, which is, I would say bad. Which is worse than 2020. So there were all these theories about why,

what is it, what's going on? I mean, something's definitely increasing the pressure on astronauts' eyes. But what is it, is it to do with lymphatic fluid that's moving around in microgravity? And NASA calculated that the equivalent of two large plastic bottles of Coke shift from your legs when you're in space towards your head. Wow. You got a lot of fluid.

I mean, there's sort of why they look a little bit like they're being choked. That's one of the main reasons I wouldn't want to go up. I think that if I face got all puffy and it was all. like congested, I would just feel so grumpy. They wouldn't invite me back anyway. No. I mean, you wouldn't do 340 days up there, would you? The thing is, is that they did a study into this in 2015, and they were looking specifically at people on the vomit comet to work out how much pressure was in their heads in that moment. And they were actually surprised to find out that intercranial pressure, right, intercranial, so inside, actually dropped during the periods of lower gravity.

Okay. So the current theory about why is all of the stuff going on in your eye. So even though your face is getting puffy and your lymph is up in your face, it's inside your head you're actually okay. Okay. So the current theory is that it's your cerebrospinal fluid. Oh. That is floating around. This is the stuff that helps to cushion your brain, by the way.

And when you are not in a sort of upright position, when you don't have gravity assisting you, that pressure is. like all over the place and your eye ends up changing as a direct result of it. Jeez. Mm-hmm. Not good, is it? Why does your face change? Because of the lymph, the lymphatic fluid. Because of the lymphatic fluid.

Exactly. Your eyeball is harmed by this cerebro spinal fluid stuff because the optic nerve goes right into the brain. Exactly. So you're like, wow. Yeah. Not good. There's more you're going to tell.

Oh, there's more. Not everybody is affected in the same way with their eyes. It affects some people worse than others. But we're talking the whole of the body is essentially like really not happy when it goes into space. I can see that this would be a big challenge for long space flights. Very definitely. We've got to come up with some artificial gravity. Yes.

Maybe some more stuff. You tell me what else goes wrong. Because this is the thing. You just don't expect that gravity would make that much of a difference. But it turns out that the earth is the reason why our bodies function in the way that we do. We are of this planet, right? We really are off this planet. We really are.

This is our womb and our crib and our world and our grave. Yeah. And we think, oh, it would be so cool to have no gravity around. And then our bodies tell us actually, this is what I was built for. What are you doing? Okay. So let me give you some examples about the ways in which our body is built for this. Body temperature is so much harder to control when you're in space.

Is it really? than it is when you're on earth. Because if you're on earth, right, you lose most of your body heat through convection. You've got air that's moving around to you. You've got cooler air. You've got that sort of movement turning on a fan on a hot day, all of that kind of thing. But on the ISS, there's no convection. Right. Because there's no buoyancy. More mare doesn't rise. More mayer stays kind of around us as an envelope around your body. Yeah. So sweat sticks to your skin as well. And astronauts take.

temperatures when they're up in space rises by about one degree C. You're constantly hot and puffy. Yeah. And you can't see. Hot and puffy. A fan would help. A fan would help, agree, because then you're mechanically moving the air. Humans have sort of outsourced a lot of our thermoregulation to the planet, which I think is a kind

of crazy idea. There's also our circadian rhythm, our sense of time, our sort of concept of days and nights just goes completely all over the place when you're up in space because because that again is tied to the orbit of our planet around the sun right and the rotation of our planet on its own axis so there have been lots of studies into this okay in the ISS they can control their lights but they've got what 17 sunrises and sunsets a day so you have to just rely on the artificial lighting in the ISS for night and day you're I want to write this down, a couple of things down, because I'm obsessed with the ways in which we offload our mind to calendars and computers and notifications and alarms.

But you're right. Even before technology, our bodies were offloading functions to physics in general. Right. I need to dump heat. Luckily, convection exists. Thank you very much. I need to not have my eyeballs get all fricked up. Luckily, gravity will keep those fluids at bay.

That's the closest I've ever heard you get to swearing. I can't believe that. If my mom hears that I said fricked, I said it again, I'm going to have to go to space. Just to get away. But also this idea of like when to rest, you know, our bodies automatically know when to rest. And that is something else that we have completely. outsource to the planet. We have.

In the form of arsacadian rhythms and daylight being the primary driver of it. There have been much longer, older studies into this about how messed up we get about the passage of time when we don't have those cues. One that I really like was in the 60s, a 23-year-old geologist got put into a cave and then just sort of left there. This is in the Ligurian Alps. about 130 meters down. I would say not a nice place to spend some time.

So it's like really cold. It depends on how introverted you are. Not really. No, it depends on how much you treasure your sanity. Yeah. It sends you completely wild. So there's a one-way phone line. He could call up and the team would not call down,

but they were instructed to never mention the time or the date whenever he called them. And every time he woke or he ate or he prepared to sleep. he would ring them so that they could log it so they had a little clock and that he wasn't allowed to see. And he just had the freedom to eat when he was hungry and sleep when he was tired and so on. Anyway, when he eventually came out,

he had been down for 63 days. Would you like to guess how long he thought he'd been down for? Yeah, hold on. My guess is that he thought he'd been down for, gosh, I don't even know, longer or shorter? I'm going to say he thought he'd been down for 90 days. Right, which would have been my guess as well. I would have assumed that it was torture

and that it just felt like time had stretched in the sense of psychologically. Actually, he thought he'd only been down for 35 days. Whoa, half as long. Yes. I mean, it's the factor of two again. It's the same as if you send your twin in a spaceship, but except you haven't actually aged for real, which I think is wild.

But basically what happened is his circadian rhythm stretched a little bit day by day by day by day until he was living not 24 hour days, but sort of 30, 40 hour days and just not even realizing that that was what was happening. Wow. But the same thing, if you're not careful,

without the light cues, without sort of the sense of time and light cues, you just cannot keep track of time. I mean, I think clocks sort of helped this as well as you say, you sort of outsource this to a clock. Yeah, yeah. So if we lived in like this room with no natural light, but we had a clock, we could still say,

oh, I think it's bedtime now. But I spent three days in an isolation room with no clocks. And the lights were on, weren't they? And the lights would never go off. Oh, gosh. And no meals were delivered, because I didn't want to ever get any clue. So all the food was there with me.

And I didn't ring anyone up because I was afraid that even if I rang up to be like, oh, hey, I've decided to go to sleep, that I could tell what time it was based on how groggy the person sounded. Right. If it was like the main producer answering, It's the middle of the day. If it was some younger production assistant, I'd be like, it's the middle of the night. Okay.

And I had them surround the whole chamber with loud fans because I didn't want to be able to hear. That sounds like someone who's doing some maintenance work. That wouldn't be happening at night. It's not night. So, but I got immediately confused. By the next day, I thought it had been two days or something. And that was only a three-day isolation. So you thought it was longer.

Yes, I thought, okay, it's definitely Sunday by now. And then down on screen, they're like, it's Friday at 11 p.m. Like, I was just way off. I would take little naps and wake up and think, oh, man, it's been a whole night. But I couldn't turn the lights out. Did you have an eye mask? No, no. But I used like the pillows and the bedding.

And I had a little, there were cameras in there the whole time too. So I had like a kind of a private-ish toilet. it. But I just meditated. I didn't have, I started playing with my sock. And I said, no, this is about nothing coming into my brain. Right. And it felt like it whizzed by looking back. At the time, then?

At the time, it felt like, is this ever going to end? Are they going to leave me in here? But I have no memories from it because nothing happened. Yeah. Oh, my gosh. I can't, I can't, I would worry that I would permanently psychologically damage my in that situation. You're much brave. I hoped I would. The opposite of worry, but I'm fine, as it turns out. As it turns out, we think, still too early to tell. Is it, is it, all right, so circadian rhythms. Yeah, your sense of time anchored to the planet. Your bones also,

by the way, are nothing extremely anchored to gravity. And what's happening is astronauts, they're losing bone at this unbelievable. rate. They just don't need it. They just don't need it because you shouldn't think of your bones as though there's this storage unit. You should instead think of it. It's almost like a bank, right? Sort of like making deposits and withdrawals all the time. And when you stop requiring these withdrawals, it just sort of decays away, right? Just stops like remaking itself. The thing is, is that the way that your skeleton exits your body, do you know this? No. You essentially urinate it out. Oh, really? So it's,

put into the liquid waste. Yes, you're pissing out your own bones. This sounds kind of fun, actually. Not going to lie. But kidney stones are a really big problem in space because that's essentially one of the things, right? As you are urinating your bones away, right? They collect in the...

Exactly, they're crystallizing in your kidneys. And the thing is, once you get back to Earth, you're still in trouble from all of this. So there was one study in 2020. which looked at astronauts a year after they'd been in space. And if they had been for six-month missions, they still hadn't recovered a year after, essentially their shin bones looked a decade older.

Wow. Than they would have been had they stayed on Earth. We need that gravity for so many things. Blood also, by the way, you are breathing out your dead blood cells as you're in space. You can tell because every time a red blood cell dies, it releases one molecule of carbon monoxide. Oh. And so you can tell how much blood is decaying in somebody by giving them a breathalyzer essentially by testing.

More CO2 in their breath. Right. More blood cells die. And space anemia is a really well documented thing that people are losing blood cells in space at a rate of one and a half times what you would be getting on Earth. Wow, one and a half times. It's a lot, isn't it? So you're urinating out your skeleton, you're breathing out.

You're breathing your blood. You can't see anything unless you've got the glasses that they've got on the ISS. You can't really sleep. You can't really sleep. You're hot. It's hot. And you're sweaty, but your sweat's not going anywhere. And your face is all puffy.

I mean, this is like, frankly, doesn't sound that great, does it? No. One good thing is your DNA's all right. You're okay. Your DNA is okay. And we know this because there was an experiment where they took some mouse sperm, freeze dried it, popped it up to the ISS, left it there. you know, just sitting in storage for a little while, brought it back down to Earth, thawed it,

thawed it, used it for IVF, put it in a mouse, absolutely, totally fine, happy mouse babies. Congratulations to them. Grandchildren, mouse babies, absolutely fine. Your DNA, fine. If it's in a sperm cell, no big deal. Happy. Okay. In your body, however, slightly different, slightly different story.

So while your DNA is, it's like a recipe of how to make the whole of you as a huge. human. The way that those genes are expressed changes in your whole body, changes all of the time, right? When you sort of, I don't know, do a lot of exercise or even going back to the bone thing, right? When you're under gravity, there'll be certain expressions that are dominant over others. When they did the testing during the twin study, when they were testing Scott's genes in space and then Mark's genes on Earth. So they described it as like a set of fireworks going off in Scott's body. Scott was the one in the ISX.

You would definitely expect to see some of these changes if you take a human and you put them in a really stressful situation. There's like lots of changes that the body is adapting to. But what was really interesting was just the sort of the scale of the magnitude and the speed of this,

but also that when he was brought back down to Earth, about 90% of these changes reversed, but 10% of them lingered. They didn't go back. They didn't go back. The suggestion for why this might be the case is that he's exposed to so much more radiation than his brother was. Oh. And this matters because these systems are things that are involved with immune function, with DNA repair, with like, you know, inflammation, with oxidative stress, with like bone formation, all of this stuff.

And this was primarily, they think, because of radiation damage. Potentially. Right. Because the thing is, is that Mark Kelly, who was on Earth, his gene expression has changed too. but because he'd lived a year. Sure. But he also had this giant atmosphere protecting him from radiation.

Right. Which is brother up in space, more exposed. Much more exposed. And that brings us then to the biggest change of all. Oh, everything you had to go far is like,

okay, yeah, sure, your face is puffy or whatever, your bones are pissing out your bones. Big deal. Big deal. Who cares? I call that Tuesday. But this one is like really,

really dramatic. Do you know what a telomere is? Yeah, it's like the end of the DNA. Exactly. It's sort of, it's best described as the cap on the end of a shoelace. Okay. Yeah. When DNA is replicating itself, you know, when cells are dividing and replicating themselves, this thing gets shorter and shorter and shorter over time. And it's actually a really good way to assess how old somebody is. So their epigenetic age, as it were, as opposed to their chronological age. Right. You want long telomies.

Got it. Yeah. You want nice and long. I mean, you're nice and young. You've got plenty more replications to go before you lose more and more of that shoelace. When Scott Kelly was in orbit, his telomeres got longer. Oh. Right. I was just going to ask, what can I do to lengthen my telomeres?

Are there any, like, snake oil salesmen selling, you know, telomere lengthening cream? Yeah. NASA. Go to space and it's NASA. Whoa. NASA is selling. So, okay, do we have any ideas why? why that's going on.

Well, okay, I should also add, it sounds really good while you're in space. You've got nice long telomeres. Isn't that lovely? Kind of makes up for all of the other horrible stuff. When he came back down to Earth, the length of his telomeres collapsed and were then shorter than they would have been before. What a rugpole. What a rug pull.

You had me ready to buy my ticket to the moon. Because this is it. Then it's like Einstein was right. You live longer when you go into space as long as you don't come home. Oh, as long as you don't come. I should say, it wasn't like all of them were suddenly way short, but he had an increased number of critically short. It sounds painful. It sounds critical, frankly.

It does sound critical. It sounds bad. It sounds bad. Okay, so the question is to why this might be the case. There's another twin study where they took two pairs of twins and they took them to Everest. Two of the twins, right, from different families, went up the mountain. their brothers stayed down the bottom of the mountain and they did the same thing. They were like doing all of this testing on them.

They had to draw blood from them while they're at the top of the mountain, which I think was apparently quite dramatic. I bet, yeah. Anyway, they saw the same thing that the telomeres elongated when they were at the top of the mountain. The same thing as you get if you're on board of the ISS, which is like a really strange thing. But once again, once they came down, it didn't end well. Right.

So the suggestion as to why this might be the case. two ways that the human body can lengthen their telomeres. One, when you're born, there's a thing called telomerase. It's an enzyme that you find in embryos. You also find it in stem cells. I mean, it does exist, but just not in the normal run of things in your, in the adult body. The other way that you can lengthen your telomeres is something called alt, which is alternative lengthening of telomeres. And this isn't rebuilding. It's more that it's using a sort of DNA trick. It's like copying the sequence from another chromosome. It's extremely rare, and you really only see it in certain types of cancer cells.

Oh. Mm-hmm. So why would that be happening to people in space at the top of Everest? Like, honestly, who knows? Sort of seems as though what is happening is this ability for your cells to lengthen their own telomeres is switched off, but kind of remained dormant unless you push. that human into a really extreme environment. Right.

At which point your body sort of starts acting like it's cancer cells. Or it starts acting like it's being born again. Like it's being, well, although it's a different, it's a different mechanism. It's a different mechanism, it's a alt, not the telomerase. That's a really important point. In both the Everest and the twin study when they were in, Scott and Mark Kelly, it was the alt mechanism. That's it, okay.

Not the young, cute little baby one. you get an embryos. Bomber for them. Bummer for them. This raises this really interesting question because it means that we know that humans can lengthen their own telomeres. And this is like a very important thing

if you're talking about lengthening people's lives. It's been demonstrated that you can force people into a situation where their telomeres lengthen. You also then everybody ended up worse off. Right? As soon as they had this happen to them, they ended up worse off. But going back to Einstein's idea

of who ends up being older, the one on the spaceship or the one on earth. This telomere thing, while you're in space, you maybe have a longer lifespan, but get back, the one who went to space is worse off. It's the opposite way around to what Einstein said. So to them, less time has passed. They may have aged visibly on the surface less, but deep in their DNA, they might actually be older. Might actually be older, right.

if you actually put them on the rocket ship that went away from 10.9 years. So who would you rather be? The twin on Earth or the twin in space? Oh, stay on Earth. Thank you very much. Much rather than stay on it. You mentioned earlier, how are we going to get people long-distance space travel if all of this stuff is going on? Yeah.

Maybe they just need to be born in space. Yep. Maybe they just need to not have the history of gravity in their midst. Okay. All right, so right, if we start delivering babies in space, they will be prepared for it. Yeah. I mean, there has been a bit of delivering babies in space, just not human babies. Not human.

Yeah, they've done like rat babies, I think. Fish as well. Oh, fish. Or in the case of the telomeres, we maybe the change we kind of like, but coming back, we don't. I mean, yeah, I think the only solution to this is that we do some pregnancy. We've got to do a lot more reproduction in space. space. We need a maternity ward in space. Yeah. Good on it, guys.

And we started this episode by saying that astronauts are willing to give themselves over for the study of science. I think a newborn astronaut, let's not be on the realms of what humans can achieve. The newborn can't consent to being an astronaut. It's all right. They're doing it for humanity. We can thank them later. We can thank them later. Find a way to lengthen their telomeres back. Yeah. It's okay. So those of us on Earth have a lot to be very, very grateful for. And we have a lot to be grateful for

to those who go out into space for us because they're living through time differently and they're changing their DNA. For us. Thank you, astronauts. And thank you listeners. Yeah. Whereas we do this show for you.

And we love doing it. So thanks for being with us today. Be sure to subscribe to us. us on YouTube or follow us on whatever platform you're using to watch or listen. And field notes later in the week. We'll see you then. Bye-bye. Bye.

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