Daniel and Jorge Explain the UniverseDaniel and Katie answer a question about building super duper long structures in space
So, Daniel, you do a lot of cooking. What is the biggest kitchen implement that you have?
Do We measure kitchen implements by size. Now is the biggest one? The most important?
It is to me, I got one giant ladle and that is the most important. What is let's talk about sheer volume? What takes up the most space for you?
Well, actually, we went out and bought a huge soup pot. Last time, we made soup for about one hundred people.
One hundred people for dinner. That's a lot.
Yeah. Well, you know, we were out celebrating solstice and you got to go a little crazy on the solstice. So we had one hundred people over for sit down dinner and we made a lot of soup.
I would rather burn my kitchen down in a ritualistic bonfire than do one hundred sets of dishes after that.
That sounds like a great way to celebrate the solstice. Actually, kitchen bonfire.
Kitchen effigy. There we go, No more washing dishes.
Hooray, it's the solstice magic. Hi. I'm Daniel. I'm a particle physicist and a professor a uc irvine and I'm not into astrology, but I do love the Solstice.
I am Katie Golden. I host podcast on animal behavior called Creature Feature, and I am super duper into Solstice magics such as logs in the house and putting stones up such that they make interesting shapes and the light hits them in just such a way.
M I see you're building Katie hinge.
Katie hinge. You know, Okay for the summer Solstice one, I actually did talk about Britta Boyne, but I also want to talk about how there's a wood hinge as well as the stone hinge. And the word hinge it actually comes from the idea of a thing hanging like a hinge hanging. So stone hinge is like hanging rocks, and wood hinge is another ancient people's way of creating basically a annual sun dial, and that was made out of wooden timber.
I just always thought they were trying to hinge their bets. I was thinking about starting a hinge.
Fund, you know, Oh my god, Well we do need to teach Daniel about the difference between a hinge and a hedge.
Well could you have a hedge hinge?
Uh? You know what, It's never been done as far as I know in gardening science, but that never doesn't mean never.
Well, okay, how about a biology one that a hedgehog hinge hedgehog hinge.
Well, you know, maybe there's a hedgehog hinge for hedgehogs looking for love.
All right, we'll hedge our bets until we get there. But anyway, welcome to the podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio in which we do not hedge our bets. We go all in on trying to understand how the universe works and explain it all to you. We tackle the biggest questions, from the very nature of the universe to the smallest questions about quantum particles and the fundamental nature of space and time and everything in between, including how to get your hedgehogs out of your hinge.
So there is a question I always get about hedgehogs, and it is how do they reproduce? And my answer is very carefully, that's a.
Very pointed answer, Katie. And people have questions about the universe. They about hedgehogs, They want about quantum particles, they wonder about quantum hedgehogs, they wonder about hinges and what ancient people saw in them. They wonder what the solstice means, and they wonder what's going on between us and distant stars. And that's all part of doing physics. You don't have to be a professional academic to be a physicist. You just have to wonder about the nature of the universe and then share that curiosity with everybody else, and we hope you share it with us. If you have a question about how the universe works, and you can find an answer on Google or chat, GPT or your friendly neighborhood physicists, please write to me to questions at Daniel and Jorge dot com. We will answer it. Everybody gets an answer in their inbox, and sometimes we take an answer and put it right here on the podcast, also because we've been missing you and we wanted to hear from you again.
So ninety nine percent of a part of cul physicists job is asking the right questions and one percent is you know, math or whatever.
And this is also got to be rooting there for NAT.
Napping is crucial, right right, And like a little bit of grant writing.
Occasionally, and so on today's episode, we'll be answering listener questions. Winter Solstice Edition, Happy holidays and New Year and Solstice. To everybody out there who celebrates whatever it is you celebrate. Today, we're going to be celebrating my answering a really fun question from a listener, A question he thought of while he was in his backyard shed, maybe building his own hinge. Here's the question from Alex.
Hi, guys, I was working in my backhout on my shed, and I was using a metal crowbar to help out one day when I just realized holding it how strong it was. So my question that came to me was, what is actually the longest physical possible crowbar made of metal that could exist in space? Is it possible that you could build one? One could exist that's long enough to stretch between stars, especially if you didn't have to worry about adding to its length with unlimited supplies, and if it was nowhere near any other gravitational objects. What would the ramifications be of having it like a crowbar where one end was light hours away from the other or even light years away from the other. It seems a bit weird to travel light speed and not get from one end to the other on one particular object.
Thank you, So you know I have a similar question but once I just saw a crow bar on the ground, I think there were some people working on something like a manhole or something sort of nearby. But also I wondered if the world operates by video game rules, which is, if you find a crowbar, is that yours? Now? Do you pick it up and put it in your inventory? Or is that still stealing?
I don't know. Maybe the world operates by checkof rules. If you find a crowbar in act one, then you're gonna have about to break into something with it in Act three.
I mean that is just video game rules.
Also exactly exactly. I used to play like King's Quest back in the day, and every time you found like a weird magic rap mushroom, you put it in your back pocket because you knew you were going to need it to solve some puzzle later on.
Get ye bucket. You're gonna need that bucket for the dragon at the end of the.
Game, exactly, and you can't go back, So get the bucket now. And Alex is wondering about like the practical limits of how big we could build something like, could you build a crowbar that's long enough that you can use it to like poke people on other planets. That that's pretty crazy, thought, Alex.
It's interesting, right, because sure you could have like a large object, but the bigger it gets. Like, there's a lot of questions here, right, we need to know about a what are crowbars made out of? Steel? Iron? Steal? And so it's like, I guess a lot of it is basically the strength, like the steal, you know, the the what steals made out of? How that would work? But also you know how even if it's made out of any material, right, Like let's say crobar made out of whatever material, the strongest, hardest material you could get, Like, is there a limit to the size of physical objects in the universe before some wacky starts happening?
Yeah, this is really fun And there's a really important lesson here about how we do physics anyway, because an important sort of often implicit step that we don't talk about when we do physics is building a simplified model of the universe. Like you want to answer a physics question, you know, like a piano is falling from a window. Is you going to squish that little doggie?
No?
Oh no, I hope the answer is no. But to answer that physics question, what you have to do is simplify at first. Because you don't care about a lot of the details. You don't care about the color of the piano, you can probably ignore the crosswinds. You build a simplified model that just contains the information necessary to.
Answer the question, like the breed of the dog for example.
Yeah we don't care, I mean we care, but it doesn't change the answer. And so the trick there is to make a model that's simple enough that you can actually answer it because you've included all the details of all the quantum particles and be intractable, but is sophisticated enough that it still provides a realistic answer. That's the sweet spot for doing physics. And the interesting thing is that that's a different model in every scenario. You can ignore the winds in this case, but if you're solving a different problem like what's going to happen to this leaf and a tornado, you can't ignore the winds. So every time you solve a physics problem, you need to ask yourself, am I including the right assumptions or the assumptions I'm making going to ruin it? And so I run into this all the time with these very long space rods.
Aly.
It turns out Alex is not the only person to think about really long rods up a lot, because people have this idea that a rod is sort of like infinitely rigid. Like if I'm across the room from you and have a dowel like a wooden stick, if I push it, then you're gonna feel me pushing it. You're holding the other end, you're gonna feel it. And people imagine that sort of happens instantaneously, that if I push on the stick on one side, you feel it instantly. And that's mostly true, and for basically every problem you're going to solve here on Earth, that's basically the case, because the information travels very, very fast. But then people wonder, all right, what if I take a rod and I build it so it's like four light years long, and I stretch it from here to Alpha Centauri and some alien is holding the other side. Can I tap on my side and use that to communicate faster than the speed of light. That's a very common question I get, And the answer is obviously no. You can't break special relativity with a dowel that's four light years long.
Even dowels have their limits.
I guess yeah, And the reason is that you've broken the assumptions. Down here on Earth, it works to assume whom Yeah, The information travels instantly. That when you push one side of the dowel, the other side moves instantly. But that doesn't work anymore when the dowel's really really long, because the time it takes now matters, because a dowel, even here on Earth, doesn't transmit information instantly. What happens when you push on one side of the dowel is that you don't immediately move the other side. You push on one side and it moves the layer of molecules that are next to the edge, which you meant the next layer, which moved the next layer, which moved the next layer. Because a dowel is not infinitely rigid, it's like a very stiff version of a tube of water or like a string. You're pushing on it and there's a wave of information that travels down the dowel. So here on Earth, you push on one side of the dowel, the other side moves very shortly afterwards, but not instantly. It takes time for that information and move down the dowel. Now, when your Dowel is four light years long. That time is no longer something you can ignore. It plays a big part in how long it takes for the information to get there. And if you ignore that, then you violating special relativity. And it seems like you could send information to the stars faster than the speed of light, which of course you can't.
This is actually the same problem from a biological perspective of having like a giant brain, right, could you have an enormous brain that could like communicate instantly, right, like some galaxy sized brain. And the problem is that the way our brains work in the same way that you talked about, how like the molecules have to push on the other molecules, like our brain is all physics based. Our whole bodies are basically a big Rubok Goldberg machine of molecules bonking into other molecules, which creates things like thought. And so if you have a say, a giant enough brain, the time it would take to like have a single thought would be incredibly slow. So the bigger the brain, the more galaxy size the brain, actually the slower it would take to have a.
Thought, Yeah, exactly. And so if you're ignoring that when you're just thinking about a small brain. You can no longer ignore that in a large brain. So the lesson is, when you're doing physics, you have to always think about what are the assumptions we're making and are those assumptions still valid for this scenario. In the case of the like five light year long rod, if you assume instantaneous motion from one side to the other, then you're assuming special relativity is broken. So you can't then go and say, oh, look, this rod breaks special relativity. Well, you assume to is broken and that's why you broke it. And so there's a lot of unpacking of those assumptions in these questions. But Alex's question is a little bit different. He's not trying to communicate with aliens. He's just trying to build a really long rod, and he's wondering, like how big could you make it? Anyway? And I think that's exactly what he's digging into, Like what would break down? What assumptions we make about building long rods would break down if we try to make one that's like a light year long, Which is a really.
Cool question, yeah, because I mean there's a lot of things that we could say, like on Earth, right, Like, we could try to build a really long crow bar and at a certain point it could collapse under its own weight. But if something's in space, we'd have to figure out what kinds of forces or how gravity would be acting on something in a way that's different from Earth, right, Like, yes, you can. You know, it's like have you ever you know whiteboard pins? Like you create a big old lightsaber out of whiteboard pins and at a certain point there's too many and it collapses. But that's all using Earth physics. So you could make a much longer whiteboard pin lightsaber out in space because gravity is not impacting it in the same way that it is on Earth. But then once you get big enough, right with this pin dowel or iron crowbar or whatever it is, something's happening. And this is where I would like you to talk.
Yeah, exactly. So let's take this question out into deep space. And the first thing the wonder is like, well, what's the biggest thing that we'd built in space so far? And that's the International Space Station. It's not that impressively long, it's about thirty six meters long, but you know, it's not very far out in space, and they're not trying to build something super duper long. I think the longest thing that's ever actually been in space, it's more like a kilometer. They build a space tether, which is like a really long wire that you dangle from a spaceship to try to like generate electrical current or to learn to steer using mechnetic fields. So, like a kilometer long's the biggest thing that we've ever put into space. But again that's also just the near Earth orbit. So let's go deeper out into space and try to build something that's really long and think about the forces involved. Like when you build a rod at a steel or even a dowel out of wood or whatever, how are you actually building that thing. Usually we ignore it and just say, oh, it's some smooth, continuous substance. But if you zoom in, the reason it takes time to propagate information along it is the same thing that's holding it together, which is the forces between those molecules. All of these objects in the end are like a mesh of modules. Yet you have these little bits of matter tied together by forces to build something larger, and it's those forces that transmit the information also limit how big something can get right and so out into deep space. What is the thing that's limiting us. Well, those forces can work. They can tie something together basically infinitely, there's no limitation there. You can just keep adding layers and layers and layers to your rod. The thing that's going to keep you from building that rod light years long or infinitely long in the end, are going to be the gravitational effects, residual as they are, and the nature of space and time itself. But let's first talk about the gravitational effects. So one effect are tidal forces. So you say, well, let's be out between the stars. AX is actually talking about something which stretches between the stars. You have like one end at one star and the other end at another star. And if you have something that's like five light years long, you can't have it that far away from stars because it's going to be big enough. There's always going to be some nearby. And remember that gravity does more than just pull on things. It can actually pull things apart. These are called tidal forces. And for example, if you're near a black hole, then your head can have a different gravitational tug on it than your feet, and that can effectively tear you apart. Like, if the black hole is pulling on your feet harder than it's pulling on your head because your feet are a little bit closer, then it's going to pull you apart because its gravity is really really strong. But if you're really really long, then you don't need strong gravity to have tidal forces. Because if one end of this rod is closer to the star then the other end, and the rod is really really long, that's going to be a very large difference in the gravitational force from one end of the rod to the other, and that star is going to tear it apart. Even if the star doesn't have really powerful gravity like black holes, the sheer length of the rod makes the tidle forces very significant.
I see. So you can't span a doll from one start to the other because of the same title forces that spaghetifies you in a black hole. But what if you took away the stars? Right? Like, could you get a like infinity rod if you took away stars and just had it existing on its own in space without hitting anything?
Yeah? Right, so's get rid of the other gravity, and you still have the issue of the gravity of the rod itself. Right, You can't build an infinitely massive rod, because eventually that thing is going to have its own self gravity. It's going to collapse into a black hole. Like, you can't just make a blob of metal and keep adding blobs of metal to it and make it as big as you want, because it's going to start collapsing. This already happens for things like planets, like the Earth is about the largest rocky planet you can make. You can add more rock to it, but that's going to mean more gravity, and it's just going to compress the Earth further. So as you add more mass to the Earth, it doesn't get any bigger, it just gets denser. And eventually you keep adding mass, you're going to end up up with a black hole. And so there is a limit to how large and how massive you can make something before it collapses into a black hole. So something self gravity will also limit how large you can make an object out of practical stuff like steel or wood.
Okay, so what about a really thin rod? Now stay with me. What if you have a rod that is like one atom per unit, right, it is like one atom thick, and then you just stack a bunch of atoms into this very long rod. Would that still be something that would at a certain point start to collapse in on itself because of gravity, Or am I already breaking some laws of physics by trying to create a one atom diameter rod.
Now you could probably make a carbon nanofiber eventually that's like one atom thick and super duper long. I don't think it's a technical problem there. But what you're going to run into is a problem with a nature space and time. And if you can get rid of gravity the nearby stars and effectively get rid of the self gravity by making this thing really really lightweight, you're going to run into dark energy. So in short distances, like the size of our Solar system of the size of our galaxy, the dominant force is gravity. It holds things together, it shapes things, it determines the nature of our universe. But over very large distances, gravity gets weaker. Right, the further you are away from something, the weaker it's gravity is. And at those distances something else takes over, which is dark energy, meaning the expansion of the universe itself. Remember that everywhere in the universe is expanding. Take any arbitrary chunk of space as time goes on, That space is getting larger. It's making new space. So between the Earth and the Sun, for example, new space is being made, but the gravity of the Earth and the Sun overpowers it. Between our galaxy and the neighboring galaxy, new space is being made, but again the gravity overpowers it. But eventually, between clusters of galaxy, dark energy becomes more powerful because you have more of these cubes of space and each one is expanding, so that adds up and gravity gets very very weak. So take Alex's super duper long, infinitely thin rod. Eventually it's going to be so long that dark energy is going to tear it apart. It's going to be creating new space between those atoms faster than those atoms can recover and bind themselves together. So you can get spaghettified by space and time.
All right, So we cannot make an infinity rod. Unfortunately, do we know, like how big something can get before the expansion of the universe starts to break it apart.
It's gonna be really really big. And remember that nearby galaxies are millions of light years away, and dark energy only really dominates between clusters of galaxies, So we're talking hundreds of millions of light years. So if you can overcome the gravity of nearby stars and overcome tidal forces completely and overcome collapsing due to self gravity, then you could still build something that's like hundreds of millions of light years long. So that's pretty good, you know what.
That sounds great. I'm gonna write a grant for U to get started building on the biggest spaghetti that one could.
Make, exact spaghetti simo.
Yeah, I bet Italy's government would fun.
That's gonna write, yes, in honor of the winter solstice. I think that's a great idea. All right, Well, thank you very much Alex for thinking big and wondering about how far we can push our concepts of distance and structure and space and time. Really fun way to explore all of those different factors, and really appreciate everybody out there who's thinking about the universe and wondering about it, and who's brave enough to write into their favorite Internet physicists to look for some answers. If you'd like to see my email in your inbox, write to me two questions at Daniel and Jorge dot com. I'd sure love to hear from you. Thanks very much, Katie for pushing the boundaries of space and time and humor today.
And thank you for signing on to my petition for Universe's longest spaghetti.
Funded funded funded. All right, Thanks everyone for listening, and tune in next time for more science and curiosity. Come find us on social media where we answer questions and post videos. We're on Twitter, This, Org, Instant and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.
