How do you navigate in deep space?

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Speaker 1: Hey, Daniel, do you remember the days before we had smartphones? I try not to think about it too much. Well, you can't live with that, Wikipedia do your fingertips? How else would I seem like an expert on anything? But no, mostly I couldn't live without the direction right. Yeah. Are you the kind of driver that needs to check them out every ten seconds? Oh? Yeah, that is me. I like to know exactly where I am on the surface of the air at all times. At all times, I need constant updates to make sure I've not gone off. Well, what are you gonna do when humans get out into space? Are you gonna get around there? I'm just gonna wait until there are enough cell towers or at least WiFi. Yeah, basic human survival needs in space, air, food, and WiFi. Hi. I'm Jorge. I'm a cartoonist and the creator of PhD comments. Hi. I'm Daniel. I'm a particle physicist, and I plan to be the one million person in space. One million there. You know there are seven billion of those, so you know you let's put it pretty far ahead in line. Yeah. Well, I don't want to be the first person, or the second person or the hundredth person, but I also don't want to be the last person. You don't want to go when it's still kind of new and fresh but not dangerous. I'm not a test pilot kind of a person. A million sounds about right. A million sounds about right, but hey, I'm flexible two million, million and a half. You know I'm not going to elbow my way in that line. Well, welcome to our podcast where you are first in line to hear this. It's called Daniel and Jorge Explain the Universe, a production of I Heart Radio where normally we take you on a mental trip around the cosmos, zooming out from the tiniest little particles that define the basic building blocks of the universe all the way out to the grandest structures that shape the nature of the cosmos itself. Yeah. I just think it was as your guide, as your personal GPS to all of the amazing and wonderful things that are in the universe and also all of the unknown things that are out there for us to discover. Do you think we're a good mental GPS. Sometimes we get lost, We get on a discussion about neutrinos and we end up talking about snack foods. Well, you know, I think detours are part of the fun of a trip. Right. I wish that my navigation like Siri would tell me, like, hey, pull over and get some chips. There's a good snack shop right here. Why not? Yeah, that should be a setting, right, suggests snacks. I like that suggests yeah, AI engineers, get on it. Not in a hurry. Should be maybe an option open to wonderful discovery. That's right. And on this podcast we try to open your mind to all the future wonderful discoveries that science will bring us. And we do that by talking about the cutting edge of science, all the questions that science has not answered, all the things scientists are trying to think ground, and all the technical problems they're trying to solve on their journey to give us the answers. Yeah, because I think sometimes to think about a journey of discovery is the journey itself, you know, and the friends you make along the way. Yeah, you know, not just where you go and what do you find when you get there? For also how do you get there and how do you how do you even know where to go when you're going? Yeah, I think people imagine that it's hard to get to Jupiter or Pluto because it's so far out there. It's just like you gotta throw a rock really far into space, but it's not just really far away. It's like very hard to find. You know. Pluto is a small rock in the vast, vast reaches of space. If you're gonna throw something in that direction, you have to be really precise. You have to really know how to aim it and have to be able to course correct along the way. And that turns out to be not so easy. It's much harder than stopping for snacks. Yeah, you know, they have good snacks and jubiter. You know, it makes a little gassy at the end, but you know it's all totally worth it, right right the Red Storm chips. I love this. Yeah. So today we're gonna be asking a question that I personally have had a lot of curiosity about over the years. I've always wondered about this question, and even more so now recently I've been rewatching all the Star Wars movies and so this is a question that's really present in my mind that I've been asking myself recently, And why is that? Are you imagining how you're going to navigate to your in law's house on the Jovian moons from your vacation place in Saturn or what inspires you to think about this? Well, my wife and I are immigrants, but we're not that that kind of alien. But no, I just kind of wondered, you know, Um, in Star Wars they always get lost or they pop up in all kinds of places, and so how do you know where you are? And how do you know where to go? Or you know, they talk about like a map of the galaxy, what does that even look like? Or how would that even be useful? Yeah, it's it's very rare that they're like, make a wrong turn. They're like, we're we supposed to turn left at that pulsar or right. I don't even really remember. It feels like that's all just sort of been integrated into the electron next they have in front of them. But those are hard problems, right, it's not necessarily trivial to figure out. Yeah, and if you think about it, in popular culture, there's only been like one TV show about getting lost in space. You mean, it was called space and you know at least you know what it's about. Yeah, So today on the program, we'll be asking the question, how do you navigate in space space, and this is a problem that's relevant to future navigation. Like imagine you are flying a spaceship with lots of people on board and trying to get everybody safely to Alpha Centauri. And it's also a question today as NASA and the E s A launched satellites to explore our Solar system. How do they make sure they get to the right spot? How do they course correct if they are off? Who does those calculations? Is that on board the satellite or back here on Earth? Are there people with protractors and pencils scribbling things furiously? How does that actually work? Yeah, because you know, space is pretty big, and it's three dementi all, you know, at least three dimensions at least, yeah that we know of that we think about right now. But it's a multi dimensional and you're out there and you know, there's no mountain to reference, no street signs. How do you get around? How do you know where to go? Do you think that third dimension is going to lead to like a lot more marital arguments in the future, Like I told you to turn up at that move man, why did you turn down? This is just like so many more ways to call new dimension to divorces. Probably no, but it is really hard and it's also vital because you're so much further away from your resources. Like these spaceships they leave Earth, they're never getting a refill, like they run out of gas because they got lost. They're just lost. So you have like a very limited window to make the moves you need to make to enter that orbit or to fly by the moon. There's no reduce, like you have a one tank and that's it. So it's absolutely critical that you don't get lost and that you figure out how to get where you need to go. Yeah, So, as usually, we were wondering how many people out there have thought about this question or even have an idea about how to navigate in space. So as usual, Daniel went out there and ask the internet to try to answer this question, how do you navigate in space? That's right, and if you'd like to participate in our virtual person on the street interviews, just shoot us an email two questions at Daniel and Jorge dot com. We would love to put your uninformed speculation on the podcast. And so think about it for a second. If you were out in space in the middle of the galaxy or in between galaxies? How would you know which way to make your way home? Here's what people had to say. Because gravity distill space and time and everything. Maybe you'd have to go. Maybe you'd have to shoot a little bit off it because as you as you go close to and an object, you'd kind of be taken into its gravitational swing. Other than that, I don't know how do you navigate through deep space to just keep a set of stars to your left and hopefully you're going the same direct action. I have no idea. Maybe like by distracting energy from the Sun, or if we're very patient, maybe with solar sales, we could navigate deep space, maybe through a pulse of a star, or like I don't know, pole stars or something. I think the only way you can navigating these spaces the way we do it now by using stars and galaxies, things that are consistent, not necessarily constellations, because that could you know, in three D space they have depth and they have angles that they are relative each other. You know, constellations do. But if you use stuff like pulsars and quasars and you know the Andromeda gag, see those things, we can coordinate ourselves using a couple of those angles, we can coordinate ourselves in deep space. I think navere taking in a deep space or americum woulds to need the bicycles of navigation. You're do either use inertial navigation, sitting time, speed, and directions from someone In a short stuff you will have to pick something like the sun and navigating reference to the sun. Let's see, if you're heading to a prime centuri, we should at least have an inbuilt special I had invisible telescopes, I mean lens and meadows and special lists and optimal path correction systems and some kind of special clocks. Navigating in deep space, I would have to assume is much like seiling the ocean. You look at the stars and see whe're at relative to the stars. After your statement that space is expanding faster than um the speed of light, or faster than light can travel through it, I really have no idea. Now I think you could go anywhere you you go. Yeah, well, hopefully you can do that, but how you do it? My idea would be to mount a big giant telescope on the top of your spacecraft, on the front and the back, so you can see where you're going and where you're where you came from. Maybe a telescope as big as hubble, because your spacecraft is going to have to be that big. After we leave the planet and learn about the like further stars that we don't see on Earth, we can pick three stars, and by keeping track of the distance between us and the stars, we can know our position. And when the stars are too far away, we can always peak three new stars that we found out about along the way in our journey. So there are a lot of ideas there. What do you think of that? Pretty good? Pretty good? I feel like people were sort of thinking about triangulation and using the stars somehow to tell where you are. I feel like that's a pretty common idea in science fiction movies and boots. It's like, oh, you just look at the stars around you, and do you know where you are and you know where to go? Or like if you look at the stars and you don't recognize things, then you're kind of in trouble. I like the I said, let's put a huge telescope on the front and on the back of your spaceship, because I want that anyway, Like, if I'm flying through space, I want a big telescope because I want to see with what stuffed around me. You know, I want to do some sight seeing when I'm out there. But what do you need one in the bag though, just to see the fit is of people that you leave behind. Well, because I mean, I guess you could turn your telescope. Maybe you're saying you'll need one telescope plus like a mount or something, but hey, more telescopes are better. Well, I feel like that is a sort of a common thing, is to look at the stars around you, and somehow you use that to orient yourself, you know, kind of like we use the North Star for a long time to kind of tell which way was north when you're out in the middle of the ocean. Is that kind of an idea that we can use at all? It is an idea that we can use. And the rest on this notion that if you have an accurate map of the stars, you can compare that to what you're seeing and look for landmarks and try to measure angles between the stars to give you a sense for where you are. For example, if two stars are almost lined up in your vision, then that tells you that you're along a line drawn between those two stars. And if you can find other examples measuring angles between stars, you can give you sort of a point in three D space for where you are at that moment. Well, I guess the problem that I have always should have thought about is like, what if you find yourself on the other side of the galaxy, how would you even recognize any of the stars because the stars are gonna look totally different from the other side of the galaxy. Yeah, if you just look at like teleported to a random place in the universe where you have no reference points, there's literally no way to know where you are because there's no absolute reference there's no like point in space that's defined in zero and you can measure your location relative to that. If you get teleported to an arbitrary point in space, special relativity says it's impossible to know where you are. You can only measure your distance relative to other stuff. So if you have no familiar references, you're totally screwed. Wow, and things are like changing in time. Also, everything's moving, so you're sort of totally lost in You're totally lost. You have. The only way to orient yourself in space is relative to known things. So if you get teleported to some part of space that's totally unfamiliar. Then you literally have no way to find your way back except for randomly exploring until you do find a landmark. And when I try that the next time I get lost and my spouse is complaining, I'm like, it's special relativity. It's it's law of the universe. It's not my fault. Daniel said, this should work. Don't you feel like smartphones must have solved this marital complaint? Right, houses don't have to argue about how to navigating anymore, and they just listened to the phone. That's right. The phone has saved a lot of marriages. Probably maybe, or maybe people are like, no, listen to my phone. Well, my phone says it's faster take the expressway using Google Maps. No way, we aren't using ways. People who argue are going to argue anyway. I guess, So I guess the phones can't fix that. Yeah, And you know, navigators in throughout history have used the stars. Like if you have sailed the oceans, then to figure out where you are in this vast sea where you can see no land marks is just to look up and look for star marks. Right, to look for the positions of stars in the sky that gives you a sense for where you might be. All right, well, let's get into the sort of the nitty gritty of this problem. And because I know you, you've told me that there are sort of several ways in which we can right now sort of calculate where we are in space, you know, barring kind of like a complete map of the entire galaxy. Um, so step us through. What's the what's the sort of the basic way that we get around in space. So the simplest way, in the dumbest way, and the worst way is basically dead reckoning. And that says you know where you started, and you started on Earth, and if you have a record of all the moves you took, you went in this direction at this velocity, you should be able to calculate where you went. Because you know, spacecraft follow the laws of physics, and we know what those laws are. We have a whole model of the Solar System, so we should be able to predict if you leave in this direction at this time, and you fire your rockets here and there, we should be able to predict where you end up. That's kind of like closing your eyes and like knowing where you are right now, closing your eyes and just by like counting your steps and how you think you turn, sort of like making it to your fridge or something like that. It's like following one of those treasure maps, like fifteen paces forward then turn left step four paces, then dig right right. And that's a little terrifying. Like if you remember the days before smartphones where people had to like actually write down directions and there were things like drive for fifteen miles then take a left right, and you had no idea is this the correct left or not? You know, yeah, yeah, and we all know how well that works. In the middle of the night when you have to go to the bathroom in total darkness, you know, you better put your hands in front of you, just in cakes. Yeah, and so sailors used to call this dead reckoning, and you know it's not terrible, like it works. Okay, we have a pretty good model of the solar system, and we have rockets, and we can even measure we don't even have to just guess. And like the effect of thrust, you can measure how much you've accelerated using accelerometers, you can measure your the direction that you ended up in using gyroscopes, So we've tried to be really careful about this, and some spacecraft in the history of you know, American exploration have used dead reckoning. But I guess it's tricky too, because you know, in space you can't count your steps, like there's nothing to hold onto to tell you how far you move. You have to you have to measure your exploration and then integrate DAD to convert to velocity, and then integrate DAT to convert it to distance. So it's like a lot of room there to get error. Yes, and you mentioned a very critical step there, which is integration, and that requires knowing the time. You can't count your steps. What you need is a very accurate clock. And the more accurate your clock, the more you accurately you can calculate how far you've gone. Right, you said I shot off in this direction of the speed, Well did you go for two point seven seconds or two point eight seconds? When you're traveling at ten thousand kilometers per second, that makes a big difference. Yeah, And when distances are so huge, right, and the stakes are so high, like you can't if you miss Jupiter by a few miles, it could be bad us. Yeah, as you're gonna do a Jupiter drive by, right, then you only get one shot at it, literally, and so it's pretty tricky. And the problem here is that errors build up, Like you make a little mistake because you turned a little too far, then you're off, and the next time you can't correct it, and so the errors just build up in the integrate and eventually you can be pretty far from where you thought you right. It literally is like walking around with your eyes closed. Yeah, exactly. So that's the most basic strategy, and you can make that more sophisticated by doing corrections. You can say, well, I'm gonna use dead reckoning. Plus I'm going to look at the stars and I'm gonna try to figure out if I'm off. And this is what like a lot of astronauts did, like Apollo eleven and follow their team. They flew to the Moon by dead reckoning, but occasionally they would check in and they would look at the stars and try to get a more precise measurement for where they were, and they would use that to correct their flight path. Really, so I guess two questions. One is why didn't they just use the moon as reference because they were flying towards it, and they could tell her they were going away from it or towards it. And the size of it too, wouldn't it tell you said of the distance? But and then my second question was, you know, can you actually use the stars to tell where you are? You can? So, yes, they were pointed at the moon. But that's pretty rough, right, And what you want to do was get to the Moon and then enter into orbit around the Moon. And that was a very precise maneuver. And just like with the spacecraft, they had a limited amount of fuel, so if they burnt their fuel the wrong time, they might not be able to make it home. I said. The fuel is very expensive to lift off the surface of the Earth, and so everything was a very tight budget, so they had to be really precise. There are no exactly you can't just pull a eui in space. That costs a lot of energy to pull ui. Like you missed the snack shop. You missed the snack shop, man, you are not going back. And yes, they did stellar navigation. They looked by I to find stars, and they measured the declination using gyroscopes and they use that to correct their calculations. A huge fraction of the time they actually spent in that module was typing data into that computer. You know, it's a complicated system. And remember the whole program was loaded into the computer before it launched, Like you didn't have guys up there, like you know, tip tapping editing the program being like I think we must change the flight path or something. They had it all built in with the opportunity for small corrections based on looking at those stars. So what do you mean declination like where the constellation was relative to the Earth or something like that. No, relative to them, Right, they had an idea for where they were, and they had an idea for if we are here, the stars should appear at this angle relative to the spaceship, and then they would measure where is the star relative to where the spaceship is pointing because I had careful gyroscopes and and those angles helped them figure out exactly where they are. All right, Well that sounds like, um it worked because they got to the a few times, So I can't argue with that. All right, Well, let's get into some of the other ways that we can navigate in space and whether or not they could help us explore the furthest switches of the Cosmos but first, let's take a quick break, all right, Dina. We're talking about navigating in space. Space, space, space, And I just wonder why there's always an echo when people talk about space, because there's no echoes in space. It's because it's cool, man, It's so cool cool. It makes it sound mysterious. It gives you a sense of literally space, right, echoes give you a sense a big emptiness. But you know that's just the um audio version of the artistic impression, which you know, I'm not a fan. You not a fan of the echoes in space. No, I'm a fan of realistic science fiction. It should give us a cent or what it's actually like to be out there. Though maybe you know, if you're in a kind of little metal box, maybe there are actually a lot of echoes, but inside I see. Well, we're talking about how to navigating space, which is a big question, you know. I feel like, you know, whenever you watch a movie like Star Wars, it's like how are they getting around? How do they know where to go? And so we talked about it one way, which is dead reckoning, Like if you know you're an Earth and you leave Earth, you can sort of track your progress, but then you also have to kind of correct your errors as you go. That's right, and a better way to do that is not just be based on your initial calculation from Earth, but it takes inspiration from how your smartphone gets you to your friend's house, which is that it gets messages from satellites. Here on Earth, we have the GPS system, which is constantly broadcasting messages. That's giving your phone an idea for where it is, and your phone figures out where it is by hearing these messages and knowing how long it took the message to get here from the satellite, and it uses that to figure out where the phone is right and it also uses like a map, like your phone knows where all the satellites should be at any time, so once it gets a signal, it sort of knows where it is, yeah, precisely in knows where the satellites are. And then it gets these messages. And the messages have a little time stamp on them. They say I sent this message at exactly this time, and if you get this message, you know, seventeen milliseconds later, then you know how far the message flew because you knew it flew at the speed of light. And you get enough of these things and you can figure out where you are. And there's an analogous system. There's GPS for deep space. There is there's a space GPS. Yeah, there's a space GPS, and it's called the Deep Space Network and NASA runs it and it basically sends messages out in deep space from three locations on the Earth, and satellites get those messages, send them back and then we can use that to figure out where the satellite is. It's like a reverse Why are you seriously, it's like a reverse GPS. It's like a reverse GPS. Yeah. What happens is you send a message to a satellite and then it comes back and you count, well, how long did it take for the message to go there and come back, And that gives you a sense for the distance. And then when the message comes it's a little bit Doppler shifted based on the speed of the satellite, and that tells you how fast this satellite is moving away from you. So it gives you a measure of the current position and the velocity of the satellite. But I guess that only works for satellites, right, like it doesn't work if from in Jupiter or does it. Well, it works for anybody that can receive these deep space messages and send them back. So it doesn't give you your position relative to Jupiter. Note, only gives you your position and velocity relative to Earth. Right, But like if you know where Earth is, what this signal help you know where you are in this solar system? No, because you can't actually do the calculation yourself. And that's one problem with this deep space network is that only Earth gets to figure it out. Earth gets your message, and then the second link gives Earth the information about where you are, and then the folks on Earth have to calculate Okay, turns out you were in this position and send it to you. So it's kind of a lot of back and forth. It's not that you can just get this message from the deep space network and figured it out yourself. The way your phone can from s GPS is one directional, right, because it comes with these time stamps. Right, So why why couldn't this work the same way? The reason is the clock. The clock on the satellite is not very good because really accurate clocks are necessary to do these calculations. Is because it's much more important to be super accurate more important than your phone's GPS, and the clocks that are on the satellites are not good enough to do this, so they have to do the calculation back on Earth and then send it to the satellite because on Earth to have these super precise atomic clocks that keep everything in lockstep. Interesting alright, So we we can't rely on the Earth to tell us where we are, like if I'm out in space, or can we can we rely on Earth to tell me where I am. Earth can figure out where you are, how far you are from the Earth, and how fast you're going, but you know, it's kind of limited. Like they can get really precise measurements of where you are up to about one meter, which is really pretty amazing, like you're out you know Jupiter distance, and Earth can measure how far away you are to within one meter based on the balance of the echo, like the signal coming back and going there and back. Yeah, just timing the echo because they have really precise atomic clocks. But what they can't do is figure out like where you are laterally, like your angle because there they don't have an echo measurement, right, and so they're the uncertainties more like four kilometers for every a U the distance between the Earth and the Sun. I see, because you know, if we're out by Jupiter, we don't shine like a star, that's right, right, Like we're not visible to the Earth, So they have no idea where we are. They just know kind of how far we are. They know how far you are, and they figure out where you are laterally basically using dead reckoning and then correcting using these radio measurements. But you know, that's a pretty big uncertainty. If you get out to like the distance of Pluto, then they're uncertainties two hundred kilometers, which is really big if you're trying to enter into the orbit of Pluto. Yeah. Yeah, that sounds like a pretty big error. Viewer off by two meters in your phone GPS, you be in a whole different state. Yeah. And so practically, what these folks do is they use landmarks in the Solar system too correct So if you're getting near Jupiter, it sund I can be like, okay, I see where Jupiter is. It can compare it to where thought Jupiter should be, and you can use that to correct. So you're like you're getting landmarks. You're like, oh, you're driving your friend's house is supposed to be a hill there. Hoops, I must be in the wrong spot passing to McDonald. I know I'm halfway there kind of thing. Yeah, And so cameras on board can give accurate measurements of nearby objects, not very far away, only very nearby. You see a big, well known asteroid, you pass the Moon or a planet, then you can correct You're no longer reliant on the messages from earthly interesting, but the satellite does that calculation or like it has to send the picture bag and then here on Earth were like, oh, it just pass Jupiter. This is where you are. Yeah, that's all done on Earth currently sends the data back and then we can get corrections. And that's one of the problems is that a lot of this stuff relies on calculations done on Earth and then these back and forth communications with the deep space network, which tie up the deep space network. You know, you're only talking to one satellite. All the other ones are waiting, so you can only talk to like, you know, a few of them at a time. And that's pretty serious because like GPS doesn't work that way. GPS just sends out its messages and all the phones in the world just kind of listen. It doesn't have to be bothered by the fact that I'm using it and somebody else is using it at the same time. But deep space network gets tied up every time a satellite needs to figure out its position. So they have a new idea for how to improve this so that it can be more like GPS. Well, how does that work? Just put more clocks in it, or yes, build a really precise clock and put it on the satellite. The most precise clocks we have are atomic clocks. These are clocks that measure little atoms doing very precise wiggles that like vibrated very specific frequency. One of the most precise things in the universe because it just happens over and over and over again exactly the same time step. But these atomic clocks are expensive and they're big, and so the reason that we don't have good clocks on satellites is because nobody's ever miniaturized them. So NASA spent a lot of time building a deep space atomic clock, basically a miniaturized version of atomic clock you can put on the satellite. And is it a lot smaller or yeah, it's a lot smaller, and it's a lot cheaper, and it's about the size of a toaster. Wow. So you wouldn't want to wear this atomic clock. It's not it's not ready for wristwatch use. If you want to be super untime to meetings and podcast recordings, I could wear an atomic clock, but it might be a little inconvenient. No, And these atomic clocks cost you know, enough fifty to a hundred thousand dollars, which amazingly is actually cheaper than some wristwatches you can buy for wearing. I never understood that. But some people spend a ridiculous amount the gold plated iPhones, right, Yeah, Well, I spent a few years in Switzerland where they have these ridiculous watch shops. You can go in and spend two hundred thousand dollars on a fancy watch. But it's like hand built with all these little levers and gears thereby, you know, dwarves underground or something I don't know, And it's not even as accurate as a toaster exactly exactly. I'll take a toaster's eye atomic watch from my wrist any day. But the idea there is if you have this atomic clock on the satellite, then it can get messages from the Deep Space Network that have time stamps on them to say we sent this message at whatever time, and you can just compare that too. It's atomic clock and they say, oh, it took x seconds to get here. I can figure out where I am myself. And that's a big step forward in what they call autonomous satellite navigation, with the satellites are just sort of driving themselves, right then, it's more like the GPS we have on our phones. Yeah, exactly, and you can just be sort of passive. The folks at home don't have to do these calculations themselves and updated to the satellite. So there are fewer links because the Deep space network is kind of sort of overburdened right now. It's got like too many things to do, is I mean time slice between too many projects. So this would really free it up, all right. Well, it sounds like things are looking good for navigating within the Solar System. So we're getting better clocks on these satellites and spacecraft, and we're also we can also use familiar landmarks like Jupiter or other planets or the Sun to sort of orient where we are within the Solar System. That's right, but then it sort of gets trickier one once we get out into space. Right, Yeah, all these things still rely on being able to contact Earth. You're getting these messages from the Deep Space Network, which is on Earth, and if you want to navigate to like Alpha Centauri or halfway across the galaxy, you don't want to be getting messages from Earth. They're gonna be way too faint. You're not gonna be able to pick remain. So you need a broader system. You need a galaxy spanning system. In order to get you out of the Solar System and still make it to McDonald's. We need like a like a capital GPS galactic positioning system. All right, Well, let's get into how you would actually navigate if you wanted to venture out from the Solar System or even go to another galaxy. But first let's take a quick break. All right. There we're talking about how did not get lost in space? Although that's such a fun show, is it? You like that show that, the new one or the old one. I like the old one, but the new one's fun watching with the whole family because you know, it's a bit of a family adventure, some family tension there, you know, you leave somebody behind. If you were frozen underwater on some alien moon, would your family stop and save you or not? Oh? Man, To me, it was almost too much family drama. I'm like, where is the space and they're getting lost in space they're like melting ice. Yeah, exactly. I thought it was good anyway, A lot of fun anyway. So, yeah, it's a problem if you go out into space, especially you can like in another part of the galaxy where the stars are in a totally different arrangement. How do you get around, how do you know where you are, and how do you know where to go? So what can we do then, Daniel? Yeah, well, what you need is some other source of signals. Either have a very accurate galactive map of where all the stars are, but as you say, these things are changing in time and we have only measurements from Earth and those positions are not that accurate. Which you really need is some sort of network of signals from all over the galaxy sending you time stamped messages. I mean, if you could design it yourself, you would have a bunch of sources around the galaxy sending you messages saying time equals one time equals two time equals three, right, and from those like the like the GPS satellites we have just now on Earth, you just have If you could just have GPS satellites all the way through the galaxy super powerful, that would be enough because you could use the nearest satellites to figure out how far you are from each one, and you need three of them to triangulate your position in three D space and then you be golden. But you know that's a trillion dollar program, right, could could you use like galaxies to orienter cell? Like you know, like if I'm in somewhere in the Milky Way, I could tell where the center of the Milky Way was maybe, and I could look for other galaxy ease out there, and so can I use that to orient myself? Yeah, And you can get a rough orientation that way, right, you can tell you know where Andrameda is relative to the Milky Way, So you can spin yourself around and tell where and Drameda is. But it's very rough, I mean, and Drameda is really far away, and so measuring its location precisely is not that helpful. We need much more precision than you can get from just like fixing the positions of other galaxies, like, yeah, that will tell you roughly. But if you want to navigate and you want to save fuel and you want to make it with your thousand frozen human bodies to Alpha Centauri or whatever, then you've got to be more precise than that. You don't want to miss by a few million kilometers, You got it, You do not, And then they start to warm up and there, you know, expecting the land in Alpha Centauri and have breakfast, and you didn't bring any months and so and so you're saying that one idea could could be, like to make these GPS satellites and put them all over the galaxy. But that's really expensive. Yeah, that's ridiculous, Like we didn't even know how to get them there, right, that's the whole problem. You're right, How would the satellites know where to go or where they are? How would we know where they are? We'd have to bootstrap them somehow. If you don't know where the satellites are, then they're not very useful right there, Like here's a signal from someplace we don't know, thank you very much. That's useless. So what you need to do is find some naturally occurring equivalent something in the galaxy that operates similar to GPS that lets you figure out where you are. And it turns out the galaxy provides is it alien satellites? Daniel, are you going for the alien button? I didn't even think about the alien button, but now I am. Now I'm wondering if aliens are using our GPS system to navigate our solar system right to us. Yes, well, if you enter the solar system that already had alien civilization and have GPS signals, then yeah, you could use it without them even noticing, because it's a passive system, right right, then maybe they're using us as a GPS exactly exactly, that's the concerned. But even without aliens, there are naturally occurring, very regular clocks in our galaxy interesting and they are called pulsars. You don't have to build them, they're already there. They are already there. We talked on the podcast before about what happens when really massive stars collapse that they blow up, there's a supernova, and then if there's enough stuff in the center of it, in the core, but not enough to make a black hole, they can form this thing called a neutron star, which is a ridiculously dense ball of matter. It's called like the mass of the Sun, but it's the size of a city. Right, It's it's like almost a black hole. It's almost a black hole. Yeah, if your star was like eighty two thirty masses of the Sun, then you're probably going to turn into a neutron star. If it was heavier than you probably get into a black hole. But some of these neutron stars are amazing because they have a magnetic field which is really intense, and the magnetic field means that there's a huge column of radiation that's spewed out from the north magnetic field and the south magnetic field. So they're like shining a really bright light of radiation in two directions in space. Right, Because the stars themselves don't shine that much, but like the chaos they cause around them with the magnetic field and all the stuff around them, then that is what glows and points in a particular direction. Exactly. There's no fusion happening inside a neutron star, but there's still an intense amount of other radiation produced, and the magnetic field funnels it into these type beams. And then if the magnetic north pole is not aligned with the spinning of the star, right, it's not perfectly aligned like on Earth. Then what you get is this neutron star that's sweeping around. It's rotating, but the direction in which its signal is beaming keeps scanning through the galg like a galactic lighthouse, you know, like a spotlight that just miss just like that, yeah, Or like just like on the top of a police car, you have this rotating red light and it never turns on or off, but it looks to you like it's flashing. So from Earth, if you look at a pulsar, it goes on off, on off, on off, on off very regularly, just like a lighthouse would or a police light, and it's not actually turning on off, it's just sort of sweeping past you. Right. So if we can use these to kind of tell where we are, like as as literally like lighthouses in space, sort of like lighthouses in space, And the reason is that they're incredibly accurate. They have about as much regularity as an atomic clock. Really, like these little particles in very special conditions and cold climates and special laboratories are very regular. But these enormous, massive spinning hunks of neutrons are also regular, and so they're basically like a very powerful galactic clock that's constantly descending out a pulse like tick tick tick. Suddenly that makes a nice guy a little more stressful. It's full of ticking clocks. But it's it's like crazy periods to right, it's not like tick tack tick. Take. It's like every twenty millis like and they're shining. There's a big variety of them, from radio pulsars down to X ray pulsars. It depends, as you say, on their period. And these ones that are very fast and like twenty milliseconds, these are the best ones to use for timing. And it's hard to imagine, like an enormous, super dense star boiled down into a tiny object that spins every twenty milliseconds. Right, It's like, hey, thousands and thousands of times a second, this huge thing is spinning. It's it's an incredible amount of energy. It's mind blowing. So we can use these because we know from Earth where they are, and so if you're out there in space, you could maybe find them by looking out, and then you can tell kind of where you are because you could recognize them. Buy what their period. Each one has its own fingerprint because of its period, and you already know where they are, so you find them, you identified and you're like, okay, this is pulsar x J seventeen or whatever. And then you listen to the pulses, you know, tick tick tick, and based on the pulses that you hear, you can tell where in the wave form you are. Now, the problem is they don't send messages like the GPS satellites. The GPS satellite say okay, it's time equals seven, it's time equals eight, and then when it gets to you, you can compare against your own clock they have. You have like synchronized clocks on each side, so you can measure how long it takes the signal to get there. That's from the GPS. Pulsars aren't as convenient. They don't have a clock built in that labels each pulse separately, so it's harder to tell exactly how long it took the pulse to get there. Right, But why do you need to know that? Couldn't you just kind of look where they are and you know the angle to you, and then use like three or four of them to kind of triangulate where you are. What you really want to know is your distance to an individual pulsar, because that defines your position on the surface of a sphere that surrounds that pulsar. And you do it for another pulsar, and then your distance is defined by where those spheres intersect, and we do it for three pulsars. Then you can figure out where your distance is exactly in three D space. You're right there. You can tell roughly where you are by the angles, but that's not precise enough. Which you really want to know is the distance to these things? Really? Why is the angle not precise enough? Because these things are really really far away, right, and so a pretty big change in the location of the pulse are relative to you corresponds to a really small change in the angle. So what you really want to know is the radial distance, not just the angle. Oh, I see, it works if you're moving a huge distances, but like you couldn't tell you like by the meter where you are, yeah, or if you're really close to something, like if you're really close to Jupiter, then it's angle relative to you has a lot of powerful information about your location. But if Jupiter is really far away, then that information loses value and all these pulsars are pretty far away. But there's actually a really cool trick to overcoming this problem of pulsars not being like GPS statelines just using because great, because I don't have the time stamp. They just have a pulse. Yeah, so all you know is where you are on the pulse. And so say these pulses are like, you know, a kilometer long, for example, So if you listen to a specific pulse, are that you could tell where you are within that one kilometer long pulse. You're like, oh, I'm at the top of it, or I'm at the bottom of it, or I mean the quiet part of it or the loud part of it. That doesn't actually tell you how far you are from the pulse are. What you know is how far you are through one pulse length, but you don't know how many more pulse lengths there are between you and the pulse are. If you know you're halfway through its pulse, then you could be half a pulse length away from the original pulsar, or you could be one and a half pulse lengths away, or three hundred forty two and a half pulse lengths away. There's an infinite number of possibilities. So instead of locating you onto a single sphere when you know the distance, it's actually given you an infinite number of spheres, each one one pulse length away, because all of those are consistent with what you're seeing. That's not as good as GPS, but you know it can still work because you can do the same thing for another pulsar and get another set of spheres, and then find a third pulsar and get a third set of spheres, And where those spheares intersect is the number of places that you could be places that are consistent with the signals you're seeing. Now that's not just one place, it's not a unique solution. There's still a few ambiguities. There's more than one possible location that's consistent with those signals, and then you have to figure out which one is yours based on where you thought you were recently, and you know other clues. I see, you're sort of converting the time stamp of these pulses to like using the speed of light to kind of tell where you are in terms of space. Yeah, exactly, and you don't know exactly how far your way you are from the pulsar, you know, like, I'm a certain number of beats of this pulsar's pulse away plus a little bit, you know, only that extra little bit. And so there's lots of different solutions, lots of different possibilities for how far you might be away from one pulsar. But if you have two or three or four, then you can narrow it down. You can say I'm a certain from this one, a certain distance from that one. It's a harder problem because these pulsars aren't nicely time stamped, but people have figured it out, and if you do all the mathematics, you can figure out where you are in the Solar system to within five kilometers. Wow, that's pretty good. That's pretty good. That's better than the two from before. Yeah, exactly, it's pretty good. And it works all the way across the galaxy, not just within our Solar system, so you can be far from even if Earth in blodes the nuclear war, you can still figure out where you are from these pulsars. Are the pulsars distributed all over the galaxy or are we only looking at the ones around us. They're distributed across the galaxy. People have done a study and they found like fifty or sixty good X ray pulsars that are distributed well enough across the galaxy that you could use them as reference points. And they've actually tried this. They've done it. They've built a little one and they fluid on the International Space Station and they tried it and it worked. Wow. Pretty cool, all right, So it sounds like we do have a GPS for the Alexy. We have a galactic Pulse source system. You should also call it GPS. It's pretty awesome. It's pretty awesome. I love this idea of like, you know, astronomers don't get to build what they want. They just get to look out there and find stuff and use it to be clever to extract the information they need. And here's another great example of just like making do with what you have. Right, it's almost like a nature and the universe made these lighthouses and put them all over the galaxy just for us to kind of used to get around. Yeah, probably not just for us, but it would be a cool science fiction universe where we actually visit one of these pulsars and discover, oh, they're artificial. Maybe they're part of some billion global positions. Oh, it is a lighthouse. It didn't occur naturally, that would be pretty awesome. That would be worth some echoes in space. Space space space space space cool cool cool. All right, Well, I feel a lot better now about Star Wars and about other science fiction movies and books. It sounds like in the future we could be using these pulsars to kind of know where we are in the galaxy and to kind of build a map of the entire place. Yeah, and as we venture out further and further beyond our solar system and try to explore other solar systems, this will be a critical way to know where we are and hopefully how to come home. Yeah, And so future space explorers flying around with their partners and spouses can not argue about where they are getting lost, which would probably make for a messy divorce out in space. Well, they'll probably still argue, like, let's not use that pulsar. That one's not reliable. Everybody's using that pulsar. You sound like you, You sound like your father. All right. Well, I hope that was interesting and gives you a little bit more of a sense that we kind of know where we are in the universe and the galaxy, and that it would be a little bit hard to get lost in space. That's right. And this idea of pulsars took decades to figure out to narrow down to make it work, and it only gives us five kilometer uncertainty. Probably somebody out there will have an even better idea for how to narrow down our edition. So have that idea today so that it's ready for us to use in twenty or thirty years. That's right. You don't want to miss those snacks, you know. If you miss that snack by five kilometers, that's that's not good eating. If you learn nothing else today. Remember there are no U turns in space or echoes, but there probably are snacks, all right. Thanks for joining us, See you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. For more podcast for my Heart Radio, visit the I Heart Radio Apple Apple Podcasts, or wherever you listen to your favorite shows.