Welcome to Tech Stuff, a production from iHeartRadio. Hey therein Welcome to Tech Stuff, I'm your host, Jonathan Strickland. I'm an executive producer with iHeartRadio, and how the tech are you. We have an episode that originally published on July first, twenty twenty. It's called It's All Relative And when I was a kid, I was convinced that Einstein's theories were these super complicated explanations of the universe that really had no real intersection with my daily life. But as it turns out, without an understanding of relativity, a lot of the technology we rely upon wouldn't work properly. And it's fascinating stuff. Hope you enjoy. The hertz unit refers to the number of repeated phenomena over the course of a second. So well, imagine that you're dribbling a basketball, so that the ball goes from your hand to the ground back up to your hand once per second. Well, you could describe your dribbling as being one hurts in frequency one full cycle per second, up down, up. Now, if you dribbled twice as fast, so that the ball went up, down, up two full times per second, then it would be two hurts. Well, we can describe lots of stuff with the unit hurts. We use it to describe sounds, in which case we're talking about the frequency at which stuff vibrates. Typical human hearing spans a range of frequencies that at the low end is at twenty hurts. That represents the lowest pitches of sounds. You get to go those deep bass notes. That's around the twenty hurts of area, and then it goes all the way up to twenty kill a hurts or twenty thousand hurts. That represents the very highest pitches that people can typically hear, and those frequencies correlate to how quickly stuff is vibrating back and forth. Now, when it comes to us hearing things, we usually mean that we're talking about the vibrations and fluctuation and air pressure, and those fluctuations and air pressure interact with our ear drums. But we can use hurts to talk about all sorts of stuff, including the processor speed of a CPU. In that case, we're really talking about the number of clock cycles per second, So you get it. This is a description of the frequency of the number of times a certain thing happens like within a second. And I also explained that we measure the rate at which we can send data using the term bits. A bit is a basic unit of digital information, and when we talk about computers, we're talking about bits in the form of a zero or a one binary information, just like your basic two way physical switch has two positions off or on. So if you hear a term like kill a bit, that means one thousand bits, and a megabit is one million bits, and a gigabit would be one billion bits. Likewise, megabits per second tells us how many million bits can move from one point to another per second over that connection. So if you've got a one hundred megabit per second connection, theoretically it would mean that up to one hundred million bits can transfer across that communication channel per second, though that's not how it works out most of the time, but that's a matter for a different episode. I didn't mention that this is different from something like megabytes. So a byte is a unit that consists of eight bits. And this gets confusing because we often describe stuff like file sizes in terms of bytes, but transfer speeds in terms of bits. So let's say that you do have that one hundred megabits per second download speed, and you want to download a one hundred megabyte file, well, that means it's not going to take one second. It's going to take eight seconds to download the file, because a megabyte is eight times larger than a megabit. And actually even that is a little bit misleading because in computer memory terms, we typically look at units of memory based on powers of two rather than powers of ten. So instead of a kilobyte being one thousand bytes, it's actually one thy twenty four bytes. And there's no standardization in the tech industry, so sometimes people will say a kilobyte and they mean one thousand bytes. Sometimes they'll say killobyte and they mean one thy twenty four bytes, and you will want to tear your hair out, and then you'll look like I do, I'm bald if you didn't know. But this episode isn't about the peculiarities of our naming conventions and the computer information age. Instead, I wanted to tackle something else that affects everything really, but in particular, we really had to suss it out in order to make certain types of satellites work properly, and this is the concept of relativity. So in this episode, we're really going to learn why an understanding of relativity is important if we want our certain satellite technologies to work, and it serves as a great reminder that technology is only really possible through an understanding of science. You can think of tech as the physical manifestation of our understanding of scientific principles, and that means if we were wrong in our understanding of science, the technology shouldn't really work. So in a way, you can think of technology that works as evidence that the scientific method is a darn good formula. Since we're talking about relativity, it means we're going to be talking about a real Einstein today. His name was Einstein, which is convenient. But before we get to Einstein, we have Galileo Galileo Galileo figure Ro. Wait No, I'm sorry, wait that's Bohemian Rhapsody. I meant Galileo Galilei. This. Galileo made an observation that if you've got two observers moving at a constant speed and direction, so they're moving at the same velocity, they will get the same results for any experiment that involves moving stuff around a mechanical experiment. This is easier to understand if we use an example, and I like one that my colleague Robert Lamb used when he wrote about relativity for HowStuffWorks dot com back in the day. He used an example of a train and a scientific ping pong ball. All right, so imagine you've got a scientist who's standing in the middle of an aisle on a moving train, and the train is moving at a steady speed in a straight line, so there are no active forces of acceleration going on here. Remember, acceleration describes a force that involves a change in velocity, so that either means a change in direction or a change in speed, or both. But in this case constant speed constant direction. Robert used nice round numbers in his examples, so he suggested that the train is moving at one hundred miles per hour. Well it's not round. If we go to the metric system, that would be one hundred and sixty one kilometers per hour. If the train stays steady to the scientist, it will feel as if that scientist is actually just standing still, just anywhere, and we're conveniently ignoring an emotion that would happen due to irregularities with the train's wheels or the train tracks or anything like that. And if this is hard for you to imagine, just think about how you feel when you're standing still or sitting still or laying down here on Earth. We know the Earth is moving through space. It is a body in motion, but when we are still relative to the Earth itself, we don't feel that motion. Assuming there's not some other weird event going on, like an earthquake, which is something separate. But back to our hypothetical train, the scientist tosses the ping pong ball down the aisle. Now, from the scientist's perspective, this ping pong ball will travel at whatever speed they threw it at. Robert actually suggests a relatively gentle toss of five miles per hour or eight kilometers per hour. The ping pong ball would bounce down the aisle, just as it would if the scientists were to toss the ball on a train that isn't moving at all, or on just flat ground. However, let's say we have a second observer who's not on the train. They're standing off to the side, and they can see through the train. To this person, it will appear as if the ping pong ball is moving very fast. Indeed, relative to this stationary observer, the ping pong ball will appear to move at the speed at which it was thrown in addition to the speed of the train itself. So if we take the two figures, we would get one hundred five miles per hour or one hundred and sixty nine per hour. This is called a Galilean transformation. Alternatively, if the scientists were throwing the ping pong ball in the opposite direction of the train's travel, so they're facing toward the back of the train, it would appear to this second observer the ping pong ball was moving at a slightly slower speed than the overall train was, whereas to the scientist on board, the ping pong ball would still be traveling at that five mile per hour speed. So this is where the term relativity comes into play. The effects observed are relative to the perspective of the observer. It's all based on the reference frame of that observer. If you're on the train, then you're just looking at a ping pong ball bouncing at a relatively slow speed down the aisle. If you're not on the train, the ping pong ball is moving quite fast, so it's all relative. Isaac Newton would follow along and say, yeah, mate, this all tracks. I don't know why he talked like that. In his Laws of Motion, Newton stated that these laws of motion should hold in an inertial frame as well as reference frame that was moving at a constant velocity relative to the inertial frame. An inertial frame, by the way, is just a frame of reference in which there are zero net forces acting upon it, so that there are no forces of acceleration in play. So in our example, the train that we talked about, that would be our inertial frame. All of this is fairly intuitive, but then we get to something really tricky. Einstein would establish that the speed of light in a vacuum is the fastest speed in our universe. Nothing can go faster than that. But hey, what if you're on a train that's traveling one hundred miles per hour and you're facing forward, you're facing the direction of travel, and then you have a flashlight and you turn on the flashlight. Well, doesn't that mean you should perform a Galileean transformation on this and say the light from that flashlight in your hands is actually traveling at the normal speed of light on board the train. But also get that boost of the trains travel, so it should be the speed of light plus one hundred miles per hour. Doesn't that make sense? While according to actual experiments performed before Einstein would come around to explain things, the answer was Nope, doesn't look like it works that way. Scientists Edward Morley and Albert A. Michelson created an experiment to measure the speed of light back in eighteen eighty seven, and actually they were looking for something else. They were looking for evidence of a hypothetical substance called luminiferous ether. Say why, all right, we'll stick with me, because in a way this does make sense. Okay, So on Earth we see waves traveling through a medium, right, Like if you look out in the ocean, you can see actual waves in the water, and the water is a physical medium through which these waves travel. Sound can't travel in space because space is effect actively a vacuum. The particles that are in space are so far apart from one another that there's no way for the vibration of one particle to come into contact and affect another particle. So sound can't travel. Sound travels through the propagation of vibrational waves. And if your stuff isn't in contact with each other, there's no way for them to have that wave propagate. So there has to be some sort of medium like air or solid surfaces or something in order for sound travel. Well, if that's the case, said the folks of the time, then stuff like light must need some sort of medium to travel through, right. I mean sound has to have something. Light must have something too. Light can definitely travel through space. I mean, that's how we can see anything, because light from the Sun travels through space to hit the Earth. So the light has to be moving through some sort of medium we cannot observe directly. This hypothetical medium was the aforementioned maniferous ether. But assuming this ether existed at all, it had to be pretty darn special because we can't feel it, we can't detect it, it creates no observable effects, So if it were real, it had to be unlike pretty much anything else we had discovered up to that point. Now, let's assume that the universe is filled with this ether stuff. The question rises, how the heck does the ether interact with all the physical stuff that's in the universe, the actual matter and also energy. After all, the bodies in space like stars, planets, moons and all that other stuff. All of that is moving, none of it is standing still, and if it is moving, it would presumably disturb this ether medium, right. I mean, if you move your hand through a pool of water, you are disturbing that water. You're making currents and eddies. So it was thought that the motion of all these elements in space would disturb the ether in some way, and hypothetically there would be some sort of ether wind. But if there were a wind, then presumably the speed of light would be affected depending upon the wind's direction in relation to the light's direction. So think of a really windy day in the real world. If you're walking against a very very tough wind, like a gale force wind, you have to power through it to keep moving forward. Now, if you're walking with the wind, like the wind is to your back and pushing you, then you get a big boost. Well, the same thing should be happening with light if ether wind were real, and so Mickelson and Morley devised a gadget that would split light into two beams, directing those beams down different paths, using mirrors in different directions, and seeing if those two beams of light would hit an eyepiece at different times. The thought being well, one of these directions would theoretically be in the same direction as the ether wind, and one would be at a cross direction of ether wind, So we should see a difference in the amount of time it takes for the light from this one source that's been split into two to arrive at an eyepiece. But that's not what they found. They observed no such effect. So if there were such a thing as ether, the stuff wasn't giving either a boost or a drag on light itself. No matter what. The light was traveling at a constant speed, which turned out to be approximately one hundred eighty six thousand miles per second or around three hundred thousand kilometers per second. Now that flew in the face of classic Newtonian physics clearly. With the example of the ping pong ball and the train, the ping pong ball has to be traveling faster than the train it's on. I mean, that just makes sense. If you were standing on the top of the very front of the train and then you threw the ping pong ball, and we ignore stuff like wind resistant, the ping pong ball would land ahead of the train, So it has to be going faster. So what the heck was so special about light and what was going on? Well, this was one of the great mysteries that Albert Einstein set his mind to unraveling, and it formed the basis of one of his great theories of relativity. And this would be the theory of special relativity, which poses that the laws of physics are in the same in all inertial frames of references. And that means the speed of light will be the same for all observers, regardless of their relative perspectives. It doesn't matter the context. The speed of light is the speed of light. Now, there's an implication to this theory that really got people scratching their heads. If the speed of light is absolutely constant, that would mean that stuff like distance and time are not. And as a heck of a brain teaser, when we come back, we'll explore this more. Let's imagine that you live half a mile away from a lovely park, and it's a half mile away in the morning, it's a half mile away. At night, it's a half mile away. On a Tuesday, it's a half mile away. On a Saturday. Half a mile is half a mile, right, it's a reliable constant in our lives. If it weren't, we could never give directions to anywhere because all the measurements and landmarks would change all the time, and our world wouldn't make sense the way it does to us now. So in our individual experiences, in our day to day lives, stuff like distance seems pretty darn reliable and fixed. So how dare Einstein come along with this theory of special relativity at nineteen oh five and say, well, yeah, but see, the speed of light is really the true constant, and for that to work, time and distance or space, in other word, words, must be somewhat mutable. Einstein positive that there is no absolute frame of reference in our universe, which means there is no place in the universe that is totally stationary. Everything is moving, which means all motion is relative. You can't really talk about moving except in reference to some other moving thing. So even as we sit still and try to meditate, we do so on a planet that is hurtling through space. We are in motion. We're all moving through space and time, and we all have a frame of reference, and each frame of reference is just as legitimate as every other frame of reference, or I guess you could say, if everybody's super, nobody is. I guess I've watched The Incredibles too many times. Well, anyway, this particular nineteen oh five theory is called special relativity because Einstein's explanation only covered special cases, that being when two inertial frames are in constant motion with regard to one another, and there can be no acceleration, so the motion had to be in a straight line at a constant speed. A change in direction or speed would be an acceleration, and to cover those instances we would have to wait a decade for Einstein to work out his theory of general relativity. We'll get to that, but we've got a lot more to say about special relativity. So Einstein was taking a different approach to the results of the experiments done by people like Michelson and Morley. The scientific world at large was essentially saying, well, this can't be right. These results can't be right. There must be something wrong with the experiment or the equipment, because we're sure this theory is correct and that ether is there. Einstein was taking a totally different perspective. He was saying, if we assume the experiments are producing accurate results, then it stands to reason that the prevailing theory is flawed and we have to figure out what the real explanation is. And this is one of those important points in science. It's that if your results in your experiment don't meet your hypothesis, it's very possible that your hypothesis is wrong. Now you need to do multiple experiments to find out and to test your equipment make sure there's not any errors there that could be causing the issues. But it does mean that you need to re examine that hypothesis, and at this time the scientific community wasn't really doing that, so Einstein did away with the ether. His explanation suggested that our observable universe has four dimensions, not that there can only be four dimensions, but rather there are four dimensions we can detect and observe, and these would be up, down, left, right, forward, backward, and then the fourth dimension, which is time. Collectively, those three dimensions are space. The fourth dimension is time, and we get the space time continuum, this intrinsic relationship between space and time or space time continuum, which also gives us dozens of Star Trek episodes that would use it as shorthand, for things are about to get really weird. Einstein positive that the speed of light is measured as constant in all frames of reference. And let's think for a second. What we mean by speed. Speed is a description of how much distance can be covered per unit of time. So a speed of one hundred miles per hour means that in one hour's time we will cover a distance of one hundred miles. That's very obvious. But if the speed of light is constant for all frames of reference, regardless of how those frames are moving relative to each other, that must mean something about space and or time is a little wonky. And let's think about our train experiment again. If you are aboard a train moving at a move one hundred miles per hour in a straight line, and you toss a ping pong ball straight up in the air, well, it's gonna go straight up and come right back down to your hand in a nice vertical line. From an outside observer who isn't on the train, it would look a little differently. You would throw the ball up at one point relative to this outside observer, and the ball would appear to move not just vertically, but horizontally before coming back down. Now, if we repeat this experiment but we use light, we really see how it gets confusing. Okay, so now you're on a train, but it's going really fast, like let's say, half the speed of light. But the speed and direction are constant. So you're on this train. You don't feel any acceleration forces because you're moving at a constant speed and in a constant direction, so your velocity remains the same. In fact, if there were no windows on the train, you wouldn't even be able to tell that the train was moving at all. So let's say you've got a laser pointer and you've got a mirror on the ceiling of the train and a foton detector on the floor of the train. You shoot the laser up at the mirror, it reflects off the mirror, and then it comes back down and hits the detector on the floor, and it registers how long it took the light to travel from your laser pointer to hit the detector. And to you, the laser makes a vertical line. All that makes sense, right, you can imagine that, But for our outside observer who's not on the train, it would appear as though the laser were actually traveling at a diagonal up to that mirror, and then a diagonal back down toward the detector. So for one observer, the one on the train, we have a straight line. It's vertical up down. For the second observer off the train, we have an angled path, sort of like how a billiard ball can hit the side of a pool table and bounce off at an angle. But this creates an apparent paradox. The path viewed by you on the train is a straight line, and by definition that is the shortest distance between two points. The path observed by the person who is not on the train is an angled line, and by definition that has to be longer. The speed of light is constant in both cases, but the distance is different between the two points of reference. And because speed is distance divided by time, if the distance is different, the time must also be different between those two points of reference. Crazy This brings us to the concept of time dilation. It also, by the way, can affect distance. The faster an object gets, the more squished it gets. So if you had this train and you were to get up to near the speed of light, the train to an outside observer would appear to be shorter than it normally would be to anyone inside the train, the dimensions would remain exactly the same. You would not suddenly see a shorter train. It wouldn't be like you were in that compressor scene in Star Wars. The train would appear to be normal only from an outside observer who is not traveling at that speed, when it appeared that the train itself was getting squished shorter. Likewise, the faster something goes with respect to some other point of reference that's important, the more quickly time appears to pass for those at the other point of reference. Or alternatively, the more slowly time seems to pass for the fast moving thing from the frame of reference of the person who's not moving fast. This gets really clunky. I know, it gets confusing. So let's talk about space travels some more, because examples actually make this way easier to explain. All right, So let's say you've built a spaceship and this spaceship can go wicked fast, like eighty percent of the speed of light, and you're gonna go on a year long jaunt out in space, and your best friend is hanging back on Earth. Now we now have our two frames of reference. We have the spaceship, and then we have the person on Earth. So let's ignore accelerative forces for the moment because we're gonna have to just focus on special relativity. We'll get to general relativity in a moment. So you're in your spaceship. You're zooming around at eighty percent the speed of light, and for you, time is passing normally. The seconds feel like seconds, minutes feel like minutes, hours feel like hours, et cetera. And you're on there for a full year. Back on Earth, time is passing normally. For your best friend who's just hanging out on Earth, they feel their seconds pass like seconds. They're minutes passing minutes, and so on. However, when we look at the two of you in reference to one another, something unusual happens. So to your best friend on Earth, it looks like time is passing very slowly for you aboard your spaceship. To you on your spaceship, it looks like time is passing super fast for your friend back on Earth. So when you do get back to Earth a year later than the two of you enter the same point of reference, things are weird. From your perspective, you've only aged a year because you spend a year aboard your SPA ship, but a little more than a year and a half has passed on Earth while you were gone. Your calendars wouldn't line up anymore. The faster you go relative to your frame of reference, the more pronounced the time dilation. Now, I do want to be clear about this, it's not really correct to say that as speed increases time slows down. You have to always relay this in terms of having another frame of reference, because within a single frame of reference, time just passes normally. There's no difference. By the way, This is also why star dates in the Star Trek universe don't make a whole lot of sense. They tried to retroactively make it make sense. But keeping time when you're on a ship that can travel at the speed of light or in the case of Star Trek, magically going faster than the speed of light and we won't even get into warp speed at all, is crazy. But being able to use that and somehow relate it to making sense on time passing on planets or space stations or whatever. That's a huge mess. But it's also outside of our episode, so we'll just leave it at that. We don't notice the effects of special relativity in most of our day to day lives, because we are not traveling fast enough relative to each other for it to be a real factor most of the time. But it does get even more weird. Were it possible to build a spaceship that could travel at the speed of light, and you were to take this sort of trip to an outside observer, time would appear to stop for you aboard your spaceship. Now if assuming this was even possible, you would still experience time in your own frame of reference as per normal, but your friend back on Earth would see that it looked like you were frozen in time. However, this is a moot point. Matter cannot travel at the speed of light, so it's more of a thought experiment anyway. However, we can actually detect time dilation with extremely accurate time measurement device like atomic clocks. In fact, we've done it in experiments. Scientists have synchronized two atomic clocks, and these atomic clocks keep incredibly accurate time down to a matter of nanoseconds, and a nanosecond is one billionth of a second, So one clock was kept stationary, you know, relatively speaking, here on Earth. The other traveled aboard a high speed aircraft, and at the end of the experiment they compared the two clocks against each other, and the one that was aboard the aircraft had measured less time than the one that stayed on the ground on Earth. Less time passed on that aircraft relative to the amount of time passing on the ground. It wasn't just that one clock was moving more slowly than the other. Literally less time was passing in reference to the other point of from the perspective of the other point of reference, that is, the difference was right in line with Einstein's calculations. Now, as we'll see, this ends up being an important point when we get to satellites. But we can't just jump on that yet. We do need to take into consideration general relativity. So, as i mentioned, special relativity only looks at frames of reference that are in a constant and consistent motion with regard to one another. There could be no change in direction or speed because that introduces accelerative forces and that changes things. So to take acceleration into account. Einstein proposed his theory of general relativity ten years after his theory of special relativity, so this would be nineteen fifteen For those who are keeping track, This theory would incorporate the force of gravity into Einstein's work, which means factoring in acceleration. So in this theory, Einstein introduced the equivalence principle, which says that gravity pulling in one direction is equivalent to acceleration in another direction. So we can actually experience this. It's easy to remember and imagine. Imagine getting on an elevator and it's going up, and as it goes up, you feel that sense of increased gravity pulling down on you as the elevator accelerates. When the elevator is going down, you feel a sense of decreased gravity as the elevator accelerates downward. So gravity and acceleration are equivalent, which means that it can also affect our measurements of space and time. Einstein hypothesized that gravity was warping space time itself. Take something that's really massive, like a huge dense star, that would warp space time around it through its gravity, and we can even observe this scientifically, scientists have measured light that has curved around massive stars. This is called gravitational lensing. Now here's another thing that gets a bit confusing. The effects of gravity on time mean that time passes differently for objects in orbit when taken in reference to time passing on Earth itself, time pass this is faster in orbit than it does on Earth. Now, again, this is a frame of reference thing, because if you were on a spaceship in orbit, your experience of time would feel exactly the way it does when you are on Earth. It's only when we look at this from two frames of reference that we see how it doesn't match up. So what does this all mean for satellites. Well, it means that satellites in orbit have a couple of different relativistic effects going on. In our frame of reference here on Earth, satellites are traveling faster than we are to maintain orbit, which means that if we compare the passing of time in each frame of reference, time would pass faster for us than for the satellite. However, due to the gravitational effect on space time, we also know that something in orbit will have time pass faster for that thing than we would experience here on Earth. So it's the opposite of the effect of special relativity in a way, and the effects of special relie relativity and general relativity don't actually cancel each other out, which means ultimately that time on a satellite and time down here on Earth are not syncd up with reference to one another. And for some types of satellites that's a problem. I'll explain more after we take this quick break to understand why relativity is important with certain satellites, let's talk about the Global Positioning System or GPS. Now, this is the satellite system that provides data back to Earth that makes it possible to get precise coordinates using a GPS receiver. So how does that work? Well, here on Earth, you could get a very imprecise idea of your general coordinates through a trilateration using signals from cell phone towers. This works on a fairly simple principle. So we know that the radio signals sent to and from cell phones travel at essentially the speed of light. So if a cell phone tower broadcasts out a short command that just requests your phone to respond back with a quick response a ping. In other words, the amount of time it would take for the ping to reach the cell tower could be used to work backward and figure out how far away the phone is from that cell phone tower. Because you know the speed of travel, right is the speed of light, so you also know how much time it took. That means you can work backward to figure out the distance between those two points. However, that's just a distance, there's no direction there. Now, if you did this with multiple cell towers, the collective data from those towers could be used to get a rough estimate of where the phone is. So let's imagine we've got a map, and on that map we've got three cell towers A, B, and C. You can see exactly where each one is. And let's say that you've got a phone that located somewhere within the broadcast range of those three cell towers. Each tower sends a ping to your phone, Your phone responds with a ping back, and you are given the amount of distance between your phone and each of those three towers. Well, Tower a's result says that you are a mile away from Tower A, so you actually have to draw a full circle around Tower A to represent all the possible points you could be that are one mile away from Tower A, So you're drawing a mile radius around Tower A. Tower B responds that you're within one point five miles of Tower B, so you have to draw a circle around Tower B to represent all the points where you could be that are a mile and a half away from it. Now, the circle from tower B in the circle from Tower A should intersect each other at two points, but that means you could be at either of those two points. Right, you could be at either overlap, so you don't have enough information yet. By coordinating with tower C, and let's say that one tells you you're within two miles, you can draw a third circle, and the point where all three circles would meet would be your general location. It's not incredibly precise, but it does give you an idea of where you are. The GPS constellation of satellites does something similar, only we have to think of this in terms of three dimensional space rather than a two dimensional map. So a satellite sends out a high frequency, low power radio signal and receivers pick that signal up. The receiver, let's say it's your smartphone, doesn't have to send data back up to the satellite, which is good because i'd be an enormous drain on your smartphone's power. So really it's just listening for these signals. Now, the receiver and satellite both run the same digital pattern relative to a specific time stamp. It's easy if we think of this as midnight. So let's say that midnight hits and and this particular digital pattern starts both on the satellite and the receiver, so they're both running the exact same pattern. The satellite beams out a signal carrying this digital pattern. The satellite is far away, so it takes a little time, you know, not much, but a little time for that signal to get to your receiver. And the lag between the pattern that's playing on your receiver and the signal of that same pattern coming in from the satellite tells the receiver how far away it is from that particular satellite, because again we know that the signal is moving at the speed of the transmission itself, and that's the speed of light, and that's a constant. So now the receiver knows how far away it is from that one satellite. And because the orbits of these satellites are predictable, the receiver has a record of where that satellite should be relative to your surface. Occasionally we have to tweak that record because stuff like gravity can pull a satellite slightly out of position over time, so that actually is something that has to be a rest on occasion. Now, this receiver will do this with at least four satellites the Y four and not three, and I gave the three cell phone tower examples. Well, it's because the clocks on satellites and the clock that's running on the device that the receiver is built into may not be and really aren't truly synchronized. And the intersection of for spheres of distance like these four spheres representing the various ranges that these satellites are finding themselves in with regard to this receiver can only intersect at one point. That's the only place they could all intersect. So if a GPS receiver's clock is not matching up to the clocks on the satellites, there will be no intersection at all. And the receiver will say, well, I can't find an intersection, so that I know that means my clock is off from all the other clocks, and it will then adjust its own clock to be an alignment so that the or spheres have a point of intersection and that is your location on Earth. Now, in order for our receivers to be able to do this, the accuracy of the atomic clocks aboard those GPS satellites has to be accurate within twenty to thirty nanoseconds. And remember a nanosecond is one billionth of a second. That is an astounding level of accuracy. And because these satellites are in motion and they are also affected by Earth's gravity, they are subject to the effects of special and general relativity, and this means we actually have to make calculations to take that into account. Now, according to special relativity and the relative speeds of satellites to a fixed point on the surface of the Earth, we would expect the atomic clock aboard that satellite to register seven fewer microseconds per day than a clock on Earth because these satellites are moving through space faster than we are, relatively speaking, so that means from our frame of reference, time is passing more slowly on that satellite than it does here on Earth. Ah. But general relativity comes into play too, and general relativity tells us that the Earth's gravity warps space time around our planet. And one of general relativity's predictions is that a clock closer to a massive object, so like a clock here on Earth, will tick more slowly than a clock that is further out from that same massive object. So the closer the clock is to the massive object, the less time it will experience it will measure compared to a clock that's further away, which is crazy, right. So taking only general relativity into account, we would see that a clock aboard one of these satellites would register more time having passed on that satellite than a clock here on Earth, meaning for our frame of reference, time is actually passing faster on those satellites than it does here for us. This would come out to about forty five microseconds a day, meaning that at the end of day one, the clock aboard that satellite would be ahead of a clock here on Earth by forty five microseconds, and this would continue day after day, with the gap growing wider every single day. Now, when we bring both special and general relativity together into consideration, we see that they don't just cancel each other out right, because we've got that seven microsecond lag due to special relativity, but we have the forty five microsecond surge due to general relativity. So in the end, we're looking at a thirty eight microsecond difference per day between a clock on a satellite and a clock here on Earth. The clocks on the satellites will get ahead of similar clocks here on Earth by thirty eight microseconds every single day. And while a microsecond is a very small amount of time, I mean we're talking at a level that we don't typically experience. We don't think of time in microseconds for our day to day lives. However, thirty eight microseconds is equal to thirty eight thousand nanoseconds, and if you're looking for an accuracy of around twenty to thirty nanoseconds, this becomes an enormous problem if we don't take it into account. And this brings us back round to something I mentioned at the top of the show. We know that Einstein was right about relativity because we have to account for it with technology like GPS. If we didn't take it into account, if we didn't factor in the effects of relativity, our GPS wouldn't work for very long at all. Our technology proves that the science is real, or else the tech would fail at what it needs to do now. In general, I think that's a great lesson to take home. There are a lot of voices out there that call science into questions, and some of them are more outlandish than others, a person who's passionately and sincerely arguing that the Earth is flat seems pretty far out there for me, because so much of our technology we've built upon and we rely upon wouldn't work if that were true. Even if you can't experience something directly, such as having a meaningful experience of time dilation, a ton of the stuff we do experience on a day to day basis is affected by this stuff, and it proves the existence and also the benefits of having the scientific method. Now I'll give a little side note on GPS to kind of wrap this up. The original GPS configuration came out of a United States Department a defense project. The original purpose was to provide positioning information for government and military, but specifically the United States and its allies, and for that reason, the US government wished to restrict access to this technology. The general line of thought was that it be better if the US didn't allow tech that could, you know, give precise coordinates for stuff like military bases or the position of various military units to people who didn't belong to those divisions. So, as a matter of national security, the US guarded this technology civilian receivers. So if you went out and you bought a GPS receiver, you could get public GPS signals, but the United States was purposefully instituting a policy called selective availability, which was an intentional degradation of public GPS signals. They were introducing errors on purpose so that GPS receivers couldn't get an accurate location. It limited accuracy to around fifty meters horizontally and one hundred meters vertically, and effectively that meant that you wouldn't really know your precise coordinates. You certainly couldn't use a GPS receiver as a turn by turn directions tool because you wouldn't even necessarily show up on the right street. You wouldn't know if you were approaching your turn or if you had already passed it. It was it was not practical for that. It was only in the year two thousand, when US President Bill Clinton directed the government to end selective availability, that civilian GPS receivers could actually get accurate data. And that's what made the modern GPS receivers and stuff like our phones possible. So before two thousand, GPS receivers didn't work very well for the average person, but it wasn't because the technology was bad, or that the science was wrong it worked that way, or if you prefer it, it didn't work properly on purpose. And that wraps up this episode about relativity and why it's important with technology, and it's not just satellite tech, but that's a big one, and it also ends up being a big thorn in the side for science fiction authors who want to write about interstellar travel at faster than light speeds, because you have to start finding alternative X nations for how that's possible, because we've come up against these limits that Einstein predicted, and so far his predictions have held true. So in order to travel faster than the speed of light, you do have to create something like warp drive, which theoretically warps space around you. So rather than traveling faster than light, you're decreasing the distance between your point of origin and your destination. It would be kind of like taking a map of the United States and saying I'm going to travel from Atlanta to Los Angeles, from one coast to the other, but instead of drawing a line from Atlanta to LA you just fold the map so that the two dots are next to each other, and then you draw a line that way. That's how warp speed is supposed to work, because it's the only way you can get around the fact that you can't really go faster than the speed of light. But that's a topic for another show. If you guys have suggestions for future topics I should tackle, please let me know. Send me a message on Twitter. The handle is text hsw and I'll talk to you again really soon. Tech Stuff is an iHeartRadio production. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.