Hello, unnecessary detail listeners, it's me, Matt Parker. Before the episode starts, I want to let you know that our next big spectacular live show, that's where... where actual humans on a stage will be in London's glamorous West End on Monday, the 2nd of December, tickets to Oriental Sale, and they're selling fast. So get over to festivalofspokener.com slash tickets and you can join up to 1,199 other detail fans. In this fantastic theater, I hope to see you there, and now on with the episode.
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Yes, and today's episode is Interstellar. Fair warning, this one is going to be a bit of a space-based mindbender. Yeah, that's my fault. I'm talking about the furthest reaches of space and how we know how far away those reaches are. It's going to be fine, just go with me. And fun fact, in my bit, time is also going to really drag on. What? Great. I like it. In a time dilation way, in a strictly accurate sense, I'll be talking about black holes and plot holes.
I've got some easier listening with some of my favourite space sounds. So, let's go Interstellar. I think we're starting with Steve and some Interstellar-like distances. So, yeah, I want to talk about the Large Magellanic Cloud, which is a satellite galaxy. So, it's not a galaxy in its own right, it's too small, and it's very close to ours. So, it's trapped within the gravitational pull of the Milky Way. So, it's not part of our galaxy, but it's not a galaxy in its own right.
So, it's like a pet galaxy that orbits our much bigger galaxy. It's like a pet. Yeah. And we can see it, right? This is a naked eye object. You can see it night. Yeah, you can, absolutely. Yeah. And to the naked eye, it might look like a little cloud until you get your telescope out and you can start to see individual stars in there.
It's a 150,000 light years away give or take, which compared to the diameter of the Milky Way, which is 100,000, so that gives you an idea of the sort of scalar things. But really, how do we know the distance to any of these things? It's a great example of just the ingenuity of scientists and the way they figure out the distance to these stellar objects. So, it starts off with a scientist called Henrietta Swan-Levit.
She was looking at stars in the large Magellanic Cloud, a specific type of star called a Sephyad variable. And so, some stars vary in brightness. They go up and down. So, that might happen over a period of several days, for example, or several months. So, you can study the increasing and decreasing brightness of these Sephyad variable stars within a reasonable time frame.
And what you noticed is that there's a relationship between the brightness of a star and how quickly its brightness varies, the periodicity of its brightness. And she was able to do that because all these stars are in the same place. They're all the same distance away. They're all in the large Magellanic Cloud. So, she can tell they're all like gravitationally bound in the same place. So, she knows they're part of this cloud. Exactly.
She's a very nice formula that links the brightness of a star to how quickly the brightness pulsates. So, can you use this information to figure out how far away the large Magellanic Cloud is? The answer is no, you absolutely cannot. But at the same time, there's another scientist called A-N-R-Hertzbrung. He's looking at Sephyad variables in our galaxy, in the Milky Way.
And because of the work of Henrietta Swan-Levit, he's able to look at one of these stars, just as an example, and say, look, I can see that this star of mine is oscillating in brightness at the same rate as one of your stars in the large Magellanic Cloud. So, we know that these two stars must be equally as bright as each other. Except that when I look at it, it appears to be that mine is brighter than yours.
And that makes sense because mine's obviously closer, because mine is in the Milky Way, and yours is in the large Magellanic Cloud. And you can use this rule called the inverse square law to work out. But if my star is 9 times brighter than your star, then your star must be 3 times further away than my star is from yours. Great. So, can we use this information to work out the distance to the large Magellanic Cloud? And the answer is still no, because here's the thing.
Steve, this would better be going somewhere, seriously. We're getting there. We're getting there, Ellen. Imagine if after all this, I was just like, so we don't know. The end. Thanks, Steve. Here's the thing. So, you've got all these cephyred variables. And we can say, hey, this cephyred variable is 10 times further away from this cephyred variable. But we don't know how far away any of them are.
But the great thing is, the cephyred variables that Hurtzbrung was looking at in our galaxy, in the Milky Way, some of them are close enough that you can use a different technique to work out the distance to it. Not the relative distance, but the absolute distance to some of those stars. And it's a technique called parallax. And you can actually experience parallax in everyday life. So, do this with me at home as you're listening and Matt and Helen, you do it as well.
Put your thumb up in front of you. So, stretch out your arm in front of you and put your thumb up as if you're giving someone a thumbs up. Close one of your eyes. And now, use your thumb to just cover something up, maybe a spot on the wall or something in a picture famous. Just cover something up. I'm going to cover up Matt's face. Thanks. Oh, because we're doing this on video conference, by the way, in case you don't know, because we're all on coronavirus lockdown.
So, Helen's covering up Matt's face. I'm covering up a nail in the wall. Now, switch eyes. You can now see that thing that you are previously covering up. Yes? Yeah. So, if you want to recover that thing, you now have to move your thumb. You have to turn your arm through some angle at the shoulder to cover up the thing that you were just covering up. There was a re-expose. Now, if you could measure that angle that you had to turn your arm through.
And if you could measure the distance between your eyes, and if you could measure the distance between your eyes and your thumb, you could use trigonometry to work out the distance to the thing that you were trying to cover up with your thumb. That's called parallax. So, could you use this technique to measure the distance to a star? With your thumb. Yeah. So, close one eye, hold your thumb up, and cover a star.
And then switch eyes, and then turn your arm through some angle to cover up the star again. Would you be able to work out the distance to that star? The answer is no. As you probably guessed. So, I'm seeing a theme here, Steve. Guys, when it all works out at the end, you're going to be so satisfied. Just to illustrate why you can't use the thumb technique.
It turns out that if you try and do that with any star that you can see in the night sky, the angle that you have to move your arm through is indistinguishable from the angle you would have to use if it was infinitely far away, because of the accuracy of your equipment, like you're using your thumb. It's really not great, is it? So, instead, you need to increase the accuracy of your equipment. So, instead of using eyes, you should use telescopes.
And you should use a really, really, really big thumb. Yeah, you've just like, you've got to use a massive thumb. No, you don't use a thumb. You also, to get more accuracy, you just have to move your eyes further apart, or in our case, you're going to move telescopes further apart. Actually, by the way, as an example, hammerhead sharks, their eyes are really far apart, that helps them with depth perception. The further your eyes are apart, the better your depth perception.
Anyway, this is how you do it. So, you get your telescope, you aim it at something in the night sky, and then you wait six months, and then you do the same thing again. But now, the earth has moved halfway around the sun. So, it's like, you've got your two eyes, but their two astronomical units are apart. So, your eyes are two different measurements, and the sun is your nose. The sun is your nose, exactly. Your eyes are the same telescope, but at different points in time.
And assuming nothing significant has changed in those six months? Yes. Because stars don't move appreciably in the sky in that time period. So, if you could keep your telescope pointing in exactly the same direction, during that six month period, then what you have to do is move your telescope through some angle in the same way that you had to move your thumb through some angle. So, it's then pointing at the star once again.
In reality, that's quite a hard thing to do because the telescope is mounted on planet Earth, which is spinning all the time. So, it's really difficult to keep your telescope pointing in the same direction. Instead, you actually reference the position of the star relative to things that are effectively infinitely far away, like very distant galaxies, for example. I'd like to register my displeasure at effectively infinitely far away. More closer to infinitely far away.
Look, it's nearly infinitely far away, Matt. Can I register my displeasure, but not having found out where this massive thumb is coming from? There's no massive thumb, Ellen. Give up the massive thumb. So, you can use parallaxing this way to measure the distance to stars that are fairly nearby. And some of those are sephiod variables. Oh, that's the star from before.
Now, we can say, look, we know how far away this sephiod variable is, but literally not just relative to other sephiod variables, we know absolutely how far away it is, and we can calculate, therefore, the distance to all these other sephiod variables based on these ones that we know. And in that way, we calculate the distance to the large Magellanic Cloud.
Now, I hate to be the one who says, it's not going to work, but you need to know the distance from the Earth to the Sun as an absolute distance. Yes, that's like calculating the distance between your eyes when you're doing the experiment with your thumb. That's something you have to know in advance, which you can do with a ruler. But knowing the distance from the Earth to the Sun is a different matter. I'm not sure how that was done, actually.
It's famously transitive Venus was used in a similar parallaxy way. There are other methods, but that was pretty much it in the late 1700s, I believe. And the issue was, we discovered that after all of Steve's clever stuff with the parallax in the orbit. So for a long time, we had just had the astronomical unit, which was the distance from Earth to the Sun. We didn't know what that was, but we could then use that relatively to work out all the other distances.
Do you know how the transitive Venus helps us to understand the distance to the Sun? It's done. If you measure it at different latitudes and you get the exact timings of when Venus contacts the disc of the Sun, it's fully inside the disc and then makes out the other side, the change in timings. And then you trigger a nometry with how far up and down the Earth you are based on the latitude.
But then you're kicking the can down the road again, because to work that out, you need to know the radius of the Earth. And how's that calculated? Well, then you keep kicking it all the way down to eventually, someone just gets a stick out and then counts their way down a road or something. And like, it's that far. So yeah, this really highlights a point that you've got all these ways of measuring the distance to things, but they rely on things below it.
And it's called the cosmic step ladder, because you can't get onto the second rung of the ladder until you first stepped on the first rung of the ladder. So like, saffian variables, that's great. You can go to these great distances. But only if you step on the rung before that, which is parallax. And you can only step on the parallax rung once you've stepped on the transit of Venus rung.
And it goes further and further out until you're measuring the distance to the edge of the observable universe, and that's using red shift. And you can't calibrate red shift until you're observing specific types of supernova that happen in distant galaxies to calibrate red shift. So you've got all these little calibrations going on. It's absolutely beautiful. This is literally a standing on the shoulders of giants situation, isn't it? Yeah, definitely.
Or standing on the shoulders of, like, I don't know, red giants. Eeeh, yeah. This is a podcast of unnecessary detail, part of the A-Cash Creator Network. I would like to play you some of my favourite interstellar sound files. For the first one, would you like to listen to the warping of the fabric of a spacetime? Would I? Yes. This is a recording from the LIGO experiment that detected gravitational waves. Gravitational waves. Gravitational waves. Gravitational waves.
They're massive. You can't miss them. I didn't work. Took them so long. This is from the LIGO experiment that measured gravitational waves for the first time. And it is this enormous experiment that just took so long to do was unbelievably detailed. But it can all be boiled down to a single sound file that you can listen to right now with your own ears. Here it is. Is that the running for the most expensive sound recording of all time? Could be.
It's either that or some of the late Beatles recording sessions. So there's two things going on there, right? This is kind of low rumbling that kind of ends with a kind of eeeh, like someone throwing up quite loudly. And then there's a second one where there's this really obvious kind of chirp sound at the end, right? It goes, woo, woo, woo, woo, yeah. Exactly. Matt did a really good impression of it then. I don't know why they spent all that money. I'm also very expensive.
But what's weird about this recording is that this is genuinely data that came in at a audible frequency. It was 35 to 150 hertz, which is within human hearing. Like it's very low, so they did have to like, revamp it up a bit. But genuinely the data that came in was audible. So that's data like just hot off the laser into the rometer. Yeah. Wow. I think we need to go to the expert to explain what gravitational waves are. And the best way to explain gravitational waves is to ask Steve.
Steve, because you made a video about gravitational waves that's really popular on YouTube, right? Yeah. So I'm just going to let you take the floor here. All right, so you might know from Einstein's description of gravity, general relativity, massive objects warp the fabric of the universe. You may have seen an illustration of that, which is like a bowling ball on a rubber sheet. But imagine hypothetically that you could instantly make that bowling ball disappear.
The fabric of the universe would become flat again, but it wouldn't happen instantaneously. Actually, the reflatting of the universe would travel outwards from where the bowling ball was at the speed of light, because everything travels at the speed of light or slower. So similarly, if you were to introduce a massive object into the universe, it would warp the fabric of the universe, but it wouldn't be instantly warped everywhere in the universe.
The warping would travel outwards at the speed of light. So now imagine you've got a massive object, but you're just moving it backwards and forwards really quickly. Well, the warping of the fabric of the universe will be moving backwards and forwards, but that backwards and forwards motion will travel outwards at the speed of light.
And so if you've got, for example, two very massive objects orbiting each other, like black holes, well, they're essentially moving backwards and forwards, like if you're looking down the line at them. So you've got these ripples in the fabric of the universe traveling outwards from these orbiting black holes. And that's what we detected. So my theory is that the sound, what you're hearing there, that chirp, is the black holes getting faster and faster as they're spinning around.
So the pitch is going up, is that right? Yeah, the thing that LIGO measured was two black holes, about 1.3 billion years ago, crashing into each other and turning into one massive black hole. And that had repercussions for the sheet of gravity of the universe, because these two black holes suddenly turned into one black hole. And the ripples were what LIGO detected? Their waves in like the physical nature of the universe.
And they basically interfered with these beams of laser light that are inside the LIGO apparatus, bouncing off mirrors. And they made a vibration that started quite slow and went very fast. And that's what's created this chirp sound, because if you get anything that starts vibrating slowly and gets faster and faster, it's going to increase in pitch. So you're going to start low and end up with a high noise. So it's literally the audible representation of two black holes combining into one.
And it sounds like RRRRRR! That's what it sounds like. It's so amazing to think that they're moving so fast that it's an audible frequency. Like the period of orbit is audible. That's amazing. Well, I love those. These black holes coalesced, what, over a billion years ago. And the gravity waves have been travelling out at the speed of light all that time. And they've arrived to Earth just as they were turning on the equipment required to detect it. What are the chances?
It literally happened a long, long time ago in a galaxy far, far away. It's not as literal as this phase displacement of the lasers. So the interference pattern that the lasers detected is what's vibrating at this audible frequency. And what's, I find really interesting is that there were some people who predicted that this was the sound that it was going to make before they detected it. Really? Yeah, yeah. So there's a whole bunch of people at MIT.
I called Scott Hughes who created this way of turning data into audio, specifically for this purpose. And I've got a clip of kind of predictions of what a chirp might sound like before they actually found one. These were the early concept chirps. Yeah, yeah. This is like a demo chirp. So let's play one of those. That's a comedy chirp. I don't know why it's so funny. It's like a wide whistle. Yeah, it's like I'm watching the clangus. Yeah. It's really good.
But also, it's significantly longer than the chirp that they detected. So you can see what happens with a decent studio producer. The universe knows best about how to create a banging track. That's all I'm going to say about that. You can tell me super nervous, go, what, what, what? I just so wish that was true. So the people working on gravitation waves, they had an idea of how a chirp would sound before they had the data.
And I found interviews with some of the LEGO scientists and other astronomers who have been encouraged to listen to their data, not just look at it, because your ears and your brain can pick up things that you can't necessarily see in data. You can hear whether something sounds like a chirp or not. Whereas you look at the data, you're like, is it a chirp? You can do loads of sums on it.
Whereas if you just shove it into something that turns it into audio, you can be like, I think we're on the right track. And it's also a way of communicating that information in a way that makes you think about clowns. Yep. I find that amazing that the human brain could be used in that way. What I find really weird is we use data sonification all the time. It all sorts of different ways. But we don't really think about it. For instance, a Geiger counter is data sonification. Oh, yeah.
Yeah, you've never thought of it like that. Each click is like detecting a particle that's tripping, I don't know, probably a carotal something. And we hear that as a click coming through a speaker. Yeah. Every time it detects a single particle decay that's in its range, in its zone, then it goes click. So that's a data sonification. A clock is data sonification because it clicks once per second. I mean, that's like, no. I'm skeptical. Yeah. I mean, some of these are looser than others, right?
They use it in different ways. And so now is a kind of data sonification, how far away is something, how quickly does the blue, blue come back to you? Heart rate monitor in ICU. So one beep for every heartbeat. That's sonification. And they used to, not many surgeons use these anymore, but they used to have pulse oxymeters, which measure how much oxygen is in your bloodstream. And it emits a tone. And that tone gets lower if the oxygenation in your blood drops.
That's the one that goes, what, what, what? It kind of does. It used to be used a lot to check a patient undergoing surgery or in intensive care, had enough oxygen in their blood. Metal detectors, do they do it? Yes. That is the change of magnetic field is detected and played out as a sound. So like, boo, boo, that's telling you what the magnetic field is of the bit that's under your detector. One of your favourite instruments, Matt, is the Theraman. Theraman, yep.
Yeah, that is the perfect example of data sonification because it is an audible representation of where the performers' hands are in relation to this like metal loop and stick that make up this weird electronic instrument. And fun fact at my wedding reception, the music was played on a Theraman with a Theraman player. Yeah. Now I know that was actually live data sonification, my wedding gets even slightly more nerdy. And it was also in a pub that only took Bitcoin.
Yeah, the reception was paid for a Bitcoin. It's worked out to be a very expensive wedding reception. Let's just all move on together, shall we? So data sonification is all around us and there are loads of space waves that have been turned into amazing audio that you can hear. But there's one that I find really interesting because there's a sound that no one's entirely sure what's caused it. But when you turn it into a sound file, it is one of the weirdest creepiest things you've ever heard.
And this is data that was collected by Rosetta, which is the probe that landed the Filet Lander on the comet 67P. But when it was about 100 kilometres above the surface of the comet, it picked up these really weird clicking sounds that they're not totally sure what's caused them. But it's some kind of vibration in the magnetic field around the comet. Like, what? And so they found this data and they speeded it up and they turned it into a sound file. And it is genuinely creepy.
I know what that is. It's a sleeping velociraptor from the Jurassic Park film franchise. Yeah, it sounds like that. Or it sounds like the noise that the alien in alien makes when it's hiding around a corner, right? Ooh. Yeah. Could it be a giant thumb? It's a bonkers. What's interesting about all these space sounds is most of the time they are falsely created. They're speeded up, they're slowed down, they're one wave turned into another type of wave.
But the gravitational wave chirp that LIGO created to display their data, that's not an electromagnetic wave being turned into sound. That is a literal ripple in the fabric of our universe that has got picked up by a laser that it vibrated at an audible frequency. That for me is so much more visceral than any other space sound. Because it's this mix of technology, human stuff, non-human stuff and space time creating something that can get into your head and make you feel something.
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WarbyParker.com slash covered. I heard interstellar and of course I thought of the 2014 film interstellar by Christopher Nolan. And I want to talk about why a plot hole in interstellar is why GPS, like our positioning systems work. And I should clarify by plot hole, it's not necessarily the plot of the film, it's more if you plotted the film on a plot. There's a bit of missing, I'm gonna make it work. Try and help. Alright, there's a missing bit to the plot.
Because I thought interstellar was one of the films that actually had like advisors and stuff. They got physicists to tell them what would actually work or not, and then they incorporated that in the story line. And I don't know if this has ever happened before in the history of scientific advisors and Hollywood, but the director stipulated for important plot reasons how the science had to work, and then the advisors just had to kind of work around that.
So now just to recap, if you've not seen interstellar, it involves some people going through a wormhole into distance space to do some stuff to save humans on the earth. And as part of that, they use a thing called a time dilation, where time can run at different speeds for different people. And that's all legitimate physics, that all works. And I like the fact in the film that they say that time has become kind of a finite resource that they can spend just like they would fuel or food.
Because if they're away for what feels like, you know, a year or so, but on earth hundreds of years have passed, then no matter what they do, it's too late for the earth. So what they do, they have to get back in a reasonable time frame. So they have to keep track of how much their perception of time is shifting relative to the earth, over exciting. The problem was that the director, Nolan, wanted to have a planet where for every hour they spend on that planet,
seven years pass back on earth. And I did quickly work it out, seven years, that's 61,361 hours. So time has to go 61,361 times slower on the planet for the plot to work. And at Urethel and they had some very good experts working on the film, their main scientific advisor was a guy called Kip Thorn. Kip Thorn, who after the film, won a Nobel Prize in physics, not for interstellar, to be fair, for their work on detecting gravitational waves.
They were part of the project. They've done incredible research into like wormholes, black holes, all these things. So Kip Thorn absolutely knows what they're talking about. And so when Nolan went to Thorn and went, right, we need this rate of time dilation, then they had to kind of reverse engineer the physics to make it work. And when I watched the film, I was like, I don't think that works. So I checked the calculations and from what you see in the film, it doesn't work.
Oh, but you think you would, like, what, how can you make time travel slow? Can you make the planet really massive? Does that work? Can it be traveling really fast? Like, what are the options? What are your parameters? Right. So you've nailed the two options. Perfect. So you've got special relativity and you've got general relativity. And special relativity is the fact that if you move fast, time goes at a different rate.
And general relativity is if you're in a gravitational field, time runs at a different rate. And people often throw relativity around, but these are two very different things. Special relativity that came out in 1905. That was kind of Einstein's early years. Einstein dropped that one first. He dropped that mixtape along with the photoelectric effect, another early classic it from Einstein. Absolutely. And I often referred to special relativity. That's the easy relativity.
And it ends up being the square root of one minus your velocity squared divided by the speed of light squared. That's it. Very straightforward. I'd love to say that it's all coming back to me, but it's really not. I'm well aware that in Steve's bet he's like, oh, the inverse square law, we haven't got time to do that. And I'm like, just quickly derive special relativity. So, you know, there's levels of involvement in this podcast.
General relativity, however, that was like late Einstein when he was already very famous. This was around 1916, 1917, and it's super difficult. My goodness. Like, space time is a full dimensional thing that we exist in and time is a dimension and all this super complex stuff. Absolutely amazing. Is this like when Dylan went electric? Exactly. It's way more complicated and a lot harder to get into. Yeah, a few. An analogy that actually works for a change.
It's great. It's great. And so when Nolan went to keep thorn and said we need this time dilation, they had two options. The easy special relativity or the more complicated general relativity. And in the film, they say it's general relativity. They say it's because of the gravitational well therein next to a supermassive black hole that time slows down so much.
Well, I put the numbers into the equation and it doesn't work. You cannot get that much time dilation from being outside a supermassive black hole. And so what kept thorn actually did was decide that the planet was so close to the black hole, it was orbiting at almost the speed of light. And if you had the planet orbiting incredibly fast, you can use special relativity to get the time dilation required.
But the film in no way shows or indicates that. But I'm prepared to accept that they were told by the director they had to make this work. And so they did. I feel like there's a certain amount of ingenuity in this to make sure that the universe of the film is consistent with the universe that we live in. Because it's a film it doesn't have to be. No, it's amazing that they put the effort in and normally in a film you just kind of hand wave.
Oh yeah, that's because of I don't know the neutrinos have mutated right there's some hand wavy in no way do they attempt to do it properly. Whereas kept thorn did the calculations to work out how close to the speed of light the planet would have to be moving. It's the most rigorous techno babble you'll ever have in a film. But don't get me wrong, some stuff they do very very well, other stuff they fudge slightly. Like the stupid robot, why was it that shape? Stupid.
I quite like the robot shape. Oh, stupid shape. Ah, stupid. You just, you just, you just, you just, you don't like the cube. You're not landing on the little, like edges of the cube. Oh, edges of like a rectangle. Sticky. So you've got material engineering concerns with the film. Steve's concerns are not physics, they're more sort of ergonomics. Yeah, stupid robot.
Okay, so apart from my concerns about the use of special and general relativity, and apart from Steve's concerns of are the corners of the robot strong enough and where the robot's thumbs? Exactly. No thumbs, no science, as we've learned. And so there's a few other slight fudges. But for the most part, they did a very very good job. And apparently it's the first film that ever had an accurately visualized black hole because they did correctly use Einstein's equations from general relativity.
So that is all, do I get me wrong? That's really cool. Yeah. They did an amazing job. Yeah, that's satisfying to know. It's just, actually, for normal stuff. Okay, so that's the film fully analysed. But what is this about GPS? Because that's something that is actually real, not a film. How does that fit in? Oh, yes. So GPS, it's often used as an example of why we should care about relativity.
And if you look around online, you'll see people saying, oh, you have to use relativity because the GPS satellites are moving very fast. And so time is passing at a different rate on those satellites because of special relativity. And if we weren't able to calculate that, then our GPS wouldn't work. And so your GPS system, which is working out where you are, and these are incredibly important. They're used in trains, so they know when they're in stations.
They're used by automatic, like, farming equipment. And even the signal is used to time stamp financial transactions. So GPS is, like, baked into our modern society now. And that's half true that they wouldn't work without special relativity. But it's not the whole story.
So if you actually do the calculations, which I did, time on a GPS satellite at kind of medium earth orbit, because it's moving so much faster than we are, it's tearing around at about 14,000 kilometers an hour, very, very fast. Time will be running slightly slower on the spacecraft to the tune of about seven microseconds per day, which is not much, but it's enough to make a difference. That actually depends slightly, by the way, on where you are on the earth.
Because if you're on the equator, you're moving faster than if you're at the North Pole, just because of the rotation of the earth. So actually, it varies slightly depending on where you are, but we can do all that maths. What people forget, though, is general relativity. Because the earth is a massive mass, right? And we are more in the gravitational well than the GPS satellites are. And so, from the GPS satellites point of view, time for us is running slower.
And so that's time dilation in the other direction. And if you run the numbers, and you can put them in the equation, and you work it out, if you were somewhere else in the solar system, looking at us on earth, and if you were not in the earth's gravitational well, our time runs at about 60 microseconds a day slower. Now, the satellites aren't all the way out of the well. They just partly out of the well.
And again, if you run the numbers, it comes out to, on the order of 45 microseconds from the satellites point of view. So the speed drags time dilation one way by about seven microseconds, but then general relativity, because the gravity drags at 45 microseconds the other way. So actually, time is going faster on the satellites than it is on the earth. And that doesn't make a difference where you are, because we're all the same distance from the middle of the gravitational well.
So it doesn't depend on the speed at all. And so actually, when everything shakes out, time on GPS satellites is going 38.4 microseconds per day faster. And we have to compensate for that to get the correct location. Could we put the satellites in a certain position where they perfectly cancel out? I thought about that, and I tried to do the calculation, and I couldn't work it out. So I put that in my calculations to do later. Basket. You should use my rule of thumb.
Hey, if it's a bit of the math that you don't understand, just cover up with your thought. No, that was gone. Yeah. All right, that's it for our interstellar adventures this time. There is a whole heap of extra links and show notes and links and whatnot and probably some more links over at festival of the spoken nerd.com forward slash podcast. Yeah, specifically there are links about measuring distant things with parallax and thumbs if you like.
There's Steve's fantastic videos about gravitational waves and you can listen to a whole bunch of my favorite space sounds. All the ones that we didn't get time for are linked in the show notes. And perhaps Matt will eventually work out the rest of his relativity calculations and he'll add them to who knows. Unlikely, we actually recommend instead of waiting for that to happen, you follow the link to an interview.
Our friend, Yuzhane Von Tonserman did previously and she was involved in actually rendering out the black hole in the interstellar and because she can actually do the calculations, that was the one bit of the movie they got perfectly accurate. Yeah, they did. And if you have any unnecessary detail for us or just want to get in touch, email us at podcast at festival of the spoken nerd.com and we're on all the social media. Come and find us. And please, please review us on iTunes.
It really does make a difference to how many people actually get to hear about this podcast. And if you want free stuff, all our YouTube channels are linked at festivalofthespoken nerd.com and you can download all of Helen's songs for free from bank camp there, linked from there as well. Including the song we put at the end of this podcast. Yes, I've got another song at Forget Interstellar.
I have written a scientifically accurate science fiction song which will come in handy if you ever do voyage to another soda system. And unlike a Hollywood movie, the time commitment for this is only three minutes. So it's definitely worth your time and contains zero inaccuracies. I want to thank Oli the Octopus for doing the music production on this. You can hear the whole thing after the credits.
And if you want to watch a very cute animated video, that's down in the show notes as well. But I think we're done here. Bye. Bye. Enjoy the links. A podcast of unnecessary detail is made by festivalofthespoken nerd. That's Helen Arnie, Steve Mold and Matt Parker. Music is by Howard Carter, designed by Adam Robinson and production is by John Harvey. My gift for you is carefully chosen. It's perfect for the couple who have everything. I'm getting us both cry genetically frozen.
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