Welcome to Tech Stuff, a production from I Heart Radio. Hey there, and welcome to tech Stuff. I'm your host, Jonathan Strickland. I'm an executive producer with I Heart Radio and how the tech are you? All right? I'm gonna start this episode with a rant that arguably is almost moot at this point and is certainly tangion shoaled to the episode, But it has to do with bookstores and how they classify types of books. Now, if you've ever been in a bookstore, like a brick and mortar bookstore, and then you've looked around at the various categories like mystery, history, romance, all that sort of stuff, chances are at some point you encountered a section that was called something like science fiction and fantasy, and you would have your swords all mixed up with your lasers. In a quick shout out to the podcast Sword and Laser, which is pretty dark and great. Ut I've always been kind of grouchy about this. I felt that while science fiction and fantasy both fall into the realm of speculative fiction, they aren't the only ones. I mean a lot of horror falls into that as well, But horror doesn't tend to be grouped with science fiction and fantasy. And of course psychological horror might not fit into speculative fiction, like a person going on some sort of rampage or something, but the kind of horror where a fear feeding alien who looks like a clown definitely falls into that category. But still horror gets its own section. So why not science fiction and fantasy? And I guess I'm touchy about this because my parents are authors. Dad in particular has written a lot of science fiction, fantasy, and horror novels, as well as mystery novels and also young adult novel You know what, Dad's written a lot of stuff, and I just thought it's weird that his science fiction books and fantasy books would appear side by side in the same section. In fact, his agent and publishers were so concerned about this that at one point he had to write under a pen name for a science fiction book so that it wouldn't be right next to his fantasy books. Now, none of that really matters for this episode, except there is an element that can be found both in fantasy books and science fiction books as well as other media that I'm going to talk about today, and that's stuff. What turns you invisible. Now, in fantasy, it might be an actual cloak, so you really have a cloaking an invisibility cloak. It might be a ring that at some point you can't have to chuck into a volcano. It might be a spell or a potion, whereas in science fiction it might be some sort of technology that's incorporated in say a spaceship, that allows it to pass undetected as it sneaks up on an enemy or encounters an alien world. Now, I thought we might talk a bit about tech intended to grant invisibility in the real world. We've got some real world examples of stuff that does this to a certain degree, though spoiler alert, we do not have a technology that can cover the entire visual spectrum of light that would work like an invisibility cloak or something. There are folks working on it, but we're definitely not there yet. However, we do have some really interesting examples that at least brush up against invisibility that we'll talk about. Now, before we dive into the various technologies, let's talk about how vision works and chat a bit about light. So, way back in the day, smarty pans philosopher types tried to suss out what is light and how does vision work. Pythagoras had the angle on some stuff, but when it came to how vision works, he ended up being a bit obtuse. Yes, I'm gonna throw in lots of puns and dad jokes. Anyway, Pythagoras thought that vision worked because we were effectively shooting out rays of vision with our eyeballs, like vision was something that came from us, extended out into the world and effectively lit the world around us with vision, and so these vision rays would go out and hit objects, which let us see them. So we were kind of like Superman with this heat vision, except we're just constantly shooting out this sort of light. And you might think, silly Pathagoras, wouldn't that mean we could all see in the dark. But maybe what he was saying is that, you know, some of this light that is invisible to us in the world, like we can't see it shooting out of everybody else's eyes, but the it's what comes out of our eyes and hit stuff that's already lit, and that's what lets us see it. And so he was just thinking it was an innate ability within the human eye and presumably animal eye as well. Epicurus had a totally different take on it. The philosopher known for emphasizing the pursuit of a happy life through eliminating fear and pain, which sounds nice, felt that objects themselves were emitting this light, that they were emitting this visible ray that our eyes could detect. So our eyes are detectors, but the objects themselves are emitting this, and that as a result, we could see light coming from the objects. Again, this doesn't really hold up when you're wandering around your house in the dark and you bark your ship on a coffee table. But what he was saying was that, all right, you're in a well lit area. Every single object that has this thing in it allows you to see it because it's emanating this energy that your eyes can detect. So a little closer to being correct than Pythagoras, but still missing stuff. Now you also had philosophers who started to get a little closer to what we know to be the truth that light can reflect off surfaces, bouncing off of them, or that it can pass through certain types of material like glass or water. But when it does, when light travels from that and hits something like the surface of glass or the surface of water, it bends, the light changes direction. Now these observations gradually lead to later smarty pants folks crafting lenses intended to bend light in specific ways. Not just you know it, not just it bends light, but I want to bend light so that it goes to this specific point. And an Arabic polymath in what is today known as Iraq even al hythem I figured that the human eye was doing the same sort of thing as a surface of glass or water. That light when it goes into the human eye would end up being directed. And also that light when it's going out in the world, it's bouncing off of objects, and it's the light bouncing off those objects that passes through the human eye against bent in a way where we can perceive it, and thus that's how vision works. This was around one thousand CE, or a d if you're using the more common nomenclature. Now. By the early seventeen hundreds we had Isaac Newton proposing that light was made of little corpuscles, little particles. In other words, that light really was made up of some tiny, tiny, tiny little piece of something. And it made some sense because light travels in a straight line, and it bounces off objects, just as a physical particle would do. Like if you had a tennis ball, then you threw it at a wall, it would bounce off the wall, and depending on the angle you threw the ball at and then that it hits the wall at, it's going to bounce in a specific way. Well, what Newton was saying, light appears to be doing the same thing. So it must be made of lots of tiny little tennis balls, although he didn't say tennis balls, but you know, just to continue the analogy. Others, however, would describe light as behaving like a wave, like a sound wave. And as it would turn out, both explanations were kind of right. Light behaves as a wave and a particle, but we wouldn't be sure about that for you know, a couple hundred years. But thinking about light as either a particle or a wave helps us understand what it's doing when it encounters other stuff. So let's start by thinking of as a ray of particles, and it's a ray that travels in a straight line until it encounters something else. And let's talk about how light interacts with stuff. So first up, as reflection, This is when light bounces off of a surface like a mirror or a tree where you our face. So light will bounce off a smooth surface at an angle equal to the angle of the incoming ray, making with the surface like there's a thing called the angle of incidents, and so you can predict what that angle is going to be if you're working with a perfectly smooth surface. This is what we call the law of reflection. However, we don't have perfectly smooth surfaces. If we did, then yes, you would see light bend in this way or reflect off in this way every single time. But we don't have perfectly smooth surfaces. Instead, we've got surfaces that have imperfections. And because of this, and because the wavelengths of light are very very very small, light will bounce off at all sorts of angles because again not perfectly smooth. This is why something like a tabletop won't disappear if you change your angle of view, right like if it if the light bounced in a very specific way because you had a perfectly smooth table, well that would mean that if you moved out of the angle of incidents, you would no longer see the tabletop because there will be no light bouncing off of it that you could see, which is kind of weird to think about, like the idea that something exists in one perspective, but at another it seems to not exist anymore. It does, you just can't see it. There are other reasons why it's gonna be don't have perfectly smooth tabletops. The big one being that if you had a perfectly smooth tabletop, there will be no friction. If you said anything on the surface of the tabletopic could slide all over the place. But we'll leave that beat. But then you've got absorption. Okay, so stuff can absorb light. Now, I'm sure you all know about the spectrum of light. We're gonna be talking about a lot in this episode. That's the old roy g biv red, orange, yellow, green, blue, indigo, and violet. That's the order that you would see if you were to see a rainbow. Well, that happens to be the spectrum of visible light. It's going from the longest wavelength red to the shortest violet. But we're gonna talk more about wavelengths in a little bit, and a lot of matter can absorb certain wavelengths of light. That means those wavelengths do not get reflected back at you when the light hits that object. For example, chromium, the stuff and rubies that makes them red, absorbs the green and blue wavelengths of light, so the only stuff that's getting reflected back is in the red wavelengths of light. So rubies appear red to us because the other wavelengths of light have been absorbed by the gem. If you had something that could absorb all wavelengths of light, it would look black, like pure black, as if there were avoid rather than you know, whatever the thing is. And there are special paints out there that absorbed nearly all visible light hitting them, and seeing stuff covered in that paint is trippy because it looks like there's just a a thing shaped void in a physical space. So one example I've seen as an apple that's been half painted uh with this special super uber black paint, and you put the apple on a little rotating pedestal, and what you'll see is that when the apple rotates so that the red of the apple starts to give way to the void black, it looks like half the apple is missing, but you're not seeing the inside of the apple. It's just the half the apple is just a black shape, and if it turns all the way around, it's like the apple doesn't exist anymore. You just see a black field in the shape of an apple. It's crazy. You could do that with a pumpkin and you would have a pumpkin shaped hole instead of a jack ol Internet Halloween, which would be super awesome in the daytime, wouldn't be so effective at night. But it is really neat stuff. By the way, there are different types of this ultra black paint out there. There's one kind that was heavily trademarked, and then someone else went and developed a similar kind, specifically because they felt it was wrong for someone to try and trademark a color. But yeah, that's that's a topic for another episode. Then we have when light goes from one transparent medium to another, when it passes through a barrier, and then what happens to it. So this would be like when light travels through air, hits the surface of water or air, and it hits a lens. That's when you get refraction. Now I'll explain what refraction is because it's very important for our discussion. But first let's take a quick break. Okay, Before the break, I was talking about refraction. Refraction is when light does pass from one medium to another and it changes speed. Now that might sound weird because everyone knows light is the fastest stuff in the universe. It is the speed limit of the universe. There is nothing faster than light. In fact, we use the speed of light as a constant. The famous equation E equals mc squared is referencing the speed of light. That's energy equals the mass of something times the square of the speed of light. So if it is a constant, how can the speed of light change? Those two things don't make sense. Well, when we talk about the speed of light as a constant, we're referring to light traveling through a vacuum, an empty medium, outer space, outer space where you've got a true vacuum. But when light hits a medium like say an atmosphere or water, or the lens of a telescope or glasses, it does slow down a little. It changes speed. It can't get faster than it can through the vacuum of space. That's the as fast as anything can go. But if it hits something like trans transparent medium, it will change speed. It slows down. Think of it kind of like walking in just the open air, like you're going out for a stroll, versus trying to walk in a swimming pool. You know, when you're in a swing pool and you're trying to walk across the pool, you feel the resistance of all that water that slows you down, Whereas when you're walking through just you know, the room, then all you're doing is walking through air. You have much less resistance and you're able to go much more quickly. It's very similar to that. So when light changes speed as it passes into a new medium, it bends. The amount of bending or angle of refraction depends upon how much slower the light will travel as it moves through the new medium. In fact, we call this the refraction index when we look at the different transparent media and we say all right, well, based upon this difference, will know how much of a bend will see in the light. So if you've ever seen like a shaft of light shining down to a a surface of water, then you're looking at like a cross section, like you can see both above and below the water. You actually see where the bend is there. Or if you want to do a really easy one, you get a glass you fill it up with water, like maybe to the halfway point. Put a straw on that glass, and then you look at the glass from the side, and you'll see that the straw appears to bend at the point where it crosses over into the water. That's because of this refraction and this refractive index and the difference between the two, and we get that that little bend there. So a lens is shaped in such a way as to bend light to a specific focal point. If we're thinking of it in the terms of rays, right, array coming in at the edge of the lens, where it is more narrow, is going to be bent a certain way. Array coming in through the center of the lens is going to go in a certain direction. And then at the very bottom of the lens, which is again perhaps more narrow we're looking at our typical lens, would then be bent in a certain way so that these these different bent rays of light will converge at a point where we can get, say, an image. This is how we create things like corrective lenses for glasses, and bending light is really the secret sauce. In most invisibility technologies or cloaking technologies. This is pretty easy to understand. There's another way to look at this, by the way, and in fact, I would argue the other way to look at it makes it even easier to understand, which is to think of the incoming light as waves and think of the lens like let's say that we've got our our regular convex lens where it's narrower at the top and bottom and thickest in the middle. Right, the wave hitting the top and the bottom, those waves are going to be slowed down less than the wave that's hinting hitting the center of that lens, because the the material is thinner at the top and bottom and thicker in the middle. So the waves at the top and bottom slow down a little bit, but not a lot. The wave in the middle slows down the most. And what you get on the other side of the lens is this converging wave, being the wave is starting to get uh smaller and smaller to a focused point because of the the speed at which it has traveled through that lens, and it converges, and that's where you get your your focal point. That's another way to think about it. It becomes really important when we start talking about invisibility technologies. All right, something else we have to know about light. It's part of the electro magnetic spectrum. As I'm sure you're all know, the visible of lights just one tiny part of of a band of frequencies that make up what we call light like light that we can see. That's one tiny slice of light. Overall. There's also infrared light, which is on one side of the visible spectrum, an ultraviolet light, which is on the opposite side. We cannot see infrared and ultra violet directly. We can create technologies that let us detect this kind of light and then see it in the sense of converting that into light that we can actually directly perceive. Right, So, if you have infrared goggles, you're not actually looking at infrared light. What you're looking at is a interpretation of infrared that's been fed into technology that gives you light that you can actually see, so that things that are really hot appear red, and things that are cooler might appear blue, that sort of stuff. But the red and blue, that's red and blue. That's not infrared. It's just it's been interpreted through the technology. However, you took the the goggles off entirely, you wouldn't be able to see anything because everything would be dark. That kind of thing. It's night vision goggles work on a similar idea. So that's where light fits. But then beyond light, you've got all sorts of different types of electro magnetism, Like you have different flavors of it if you would, like you've got radio waves that's on the the longest wavelength side of the electromagnetic spectrum, and then on the opposite side, on the shortest wavelength side, you have gamma radiation. So what determines the nature of this electromagnetism, what determines what it can do and what we can use it for, is its wavelength or its frequency. The two are related. The longer the wavelength, the lower the frequency. The shorter the wavelength, the higher the frequency. But here's the thing. All of these frequencies are traveling at the same eat. That electromagnetic speed is the speed of light, so they're all traveling at the same speed. It's just that they have different lengths of of waves, right. So radio waves are very very very long, gamma waves are very very very short. They both travel at the speed of light. But it means that the number of waves that pass you in a given second are very different for radio than it is for gamma, because more of the gamma can pass you in the second than the radio waves because the length is so much shorter. Well, since visible light occupies a range of frequencies, we can encounter some challenges when we start to think about ways to manipulate light. So there's this effect called chromatic aberration. Sometimes it's called chromatic distortion, which be a great name for a band. Maybe you just cover social distortion songs. Anyway, Chromatic distortion occurs because visible light is made up of a band of wave wavelengths of light. You know, red has the longest wavelengths invisible light, Violet has the shortest wavelengths, and when light hits a refractive surface like a lens, not all these wavelengths are going to bend at quite the same angle. So you might notice that some parts of an image have little borders or fringes of color around them. And that's because that wavelength of light, let's say it's red, bent at a slightly different angle from the other wavelengths, and so you get this kind of halo effect. Now, the reason I bring this up is that one of the biggest challenges when it comes to creating invisibility technology is that the methods we might use could work differently with some parts of the visible light spectrum from others, and you might end up with the technology that can redirect certain parts of the visible spectrum in a specific way, but not all of the visible spectrum. And that would mean that you would still be able to see the cloak or the cloaked object, but it would look kind of funny because you wouldn't see all the colors you normally would, or it would appear to be a different color than what it quote unquote really is. If you want to think about another way, imagine that you've got a gap that's just wide enough to let visible light from green to violet go through. So anything that's green to violet and the visible spectrum can pass through this tiny little gap. But that would mean that wavelengths that were in red, orange, and yellow light because of roy g BIV, those wavelengths would bounce off because the gap is too small for these wavelengths to pass through it. It's it's too narrow. That's kind of what I'm going with here, all right, So when we come back, we're going to talk about some of the technology is meant to make something invisible, and we're gonna start with stealth technology after we take this quick break. All right. I'm I'm a kid of the seventies and eights, and I remember when the stealth bomber was becoming big news. It was such a cool science fiction technology. We had heard about things like cloaking devices and stuff, but here was a plane that could at least what we were told passed invisibly for radar systems. So clearly stealth technology, like the famous stealth bomber, you know, is not invisible to the naked eye. We can see it. It's not like it's Wonder Woman's invisible jet here. So we're talking about a vehicle that won't show up on radar, but we can still see it. That's because radar is operating in a different band of frequencies in the electromagnetic spectrum then visible light. Right, So if there's something in a direction, you've got a radar emitter. The radar emitter is shooting out electromagnetic waves, and if that something is there, some of those waves are going to hit that something and bounce back. So if in addition to the emitter. You have a detector that can detect the echoes of these electromagnetic waves you've sent out, then you know, hey, there's something there, right, And if you actually measure the difference in time it took for the waves to go out and then bounce back, you know how far away it is because you know how fast those electromagnetic waves are traveling. So you measure the amount of time it took for the waves to go out and bounce back, that tells you how far away the object is. You also can figure out whether or not the object is moving towards you or moving away from you because of the old Doppler effect. So if the object is moving away from you, the returning waves will actually be longer than what you sent out toward it. If it is moving towards you, then the returning waves are going to be shorter than what you sent out, and the amount of elongation or shortening would tell you how quickly this thing is traveling. So it's really interesting, like that's that Doppler effect also very important to what we're going to talk about in just a bit. So let's say that you wanted to create an aircraft that could go undetected by radar. What do you do well, You probably use a combination of strategies. So you might use some materials that can absorb electromagnetic waves in the frequencies that are being used by radar, so that way, when the wave hits the aircraft, the aircraft absorbs that energy and there's not enough to echo back to the detector, so it just it just gets swallowed up. This would be kind of that super black paint we were talking about earlier, where it absorbs most of the visible light. In this case, it would be absorbing the radar electromagnetic energy. But you probably all start going to play a bit with reflection, and you do this by designing your aircraft's exterior with these funky angles on them, so that if a radar beam does hit the aircraft, it gets reflected in an odd direction because of that angle that it hits. You know, the angle of incidents where the wave hits the aircraft means that it's going to get reflected off in a direction where hopefully there's no detector, so no one can see that there's an aircraft there. This combination of strategies makes it very difficult for radar stations to detect stealth aircraft, though again the aircraft itself itself is still totally visible to us because it's not redirecting or absorbing visible light. It's doing it in say the microwave range. Over time, as scientists develop new approaches to manipulating, absorbing, and reflecting electromagnetic radiation, we would find ways to make objects quote unquote invisible to specific kinds of electromagnetic frequencies. But it's a very different thing to make an object undetectable from say a microwave a mitter, than it is for visible light. Now, imagine for a moment that you could redirect light around an object, so the light would curve around an object, move around to the other side, and then continue on as if there were no object for the light to interact with at all. So it's not passing through whatever is cloaked, it's just going around whatever is quoaked and then getting back on track. Then an outside observer would not see anything there, right, They just look and it would just look like empty space. You'd be looking at everything that's on the other side of the object from your point of view, and that would be it. That would be really cool. Also would be very tricky because if you're making all the light curve around the object, and I'm saying all the light that's coming curves around it, that means inside you wouldn't be able to see anything. It would be perfectly dark because all light that's coming to you has been redirected. So let's say that it's like a small structure and you're inside it. It would be completely dark inside that structure because all the incoming light has been redirected. You could potentially light something inside the structure and thus be able to see And if the structure is not allowing light to pass back out, then you'd be able to see inside, but you wouldn't be able to see the outside world. Nothing in the outside world would be visible to you because all that light has been redirected. You would have to have a way to allow some of the light from the exterior world to come through, but still pass enough of the light around so that an outside observer would be unaware there was something there. That's super duper tricky. It's one of the hardest parts of the cloaking device, one of not the only so wicked hard to do. As it turns out, now we've seen some fun approaches this kind of a thing that that do succeed in certain frequencies like the microwave range. Uh. And we've also seen some fun ways to simulate a cloaking device, but it's not actually a cloaking device. For example, a fun one I have seen is a screen mounted on say the side of a truck, like like a semi truck or something along those lines, And you've got a screen on one side of display, and on the opposite side of the truck you have cameras mounted to capture a live feed of whatever is on the other side of the truck, and then it feeds that live feed to the screen that's mounted on the side, So the truck is totally solid. Light is not passing through it or going around it. Instead, you're just looking at a video feed on whatever is the other side displayed on the truck ruck. And I've seen this sort of thing at various events where it's just kind of fun, like you can actually see people walking on the opposite side of the truck, but it's because they're being displayed on this screen. It's not that the truck is actually transparent or has magically disappeared, and it's a fun effect, or it can be, but it's very limited and you know exactly what's happening, right, It's not like it's mysterious. Now. I have seen this incorporated into costumes in a way that was kind of fun. I saw a guy in a zombie costume once where he had mounted a tablet inside his costume in the front, and he was had a camera mounted on his back and it was feeding live video from the camera on the back to the tablet so that it looked like there was a hole in his torso. Like his torso just said this fist shaped hole all the way through, and that you can see video from the opposite side feeding through on the tablet, which was effective if you're looking at him at on. If you're looking at them from an angle, it didn't work so well, but it was a really clever use of this particular approach. Still not really a cloaking device. Right. To get into the possibility of actually bending light around an object, we have to talk about some really advanced technology, and I'm talking about stuff like meta materials and nanotechnology. So first up is meta material. What the heck is a meta material? I've never met a material I didn't like, No. Essentially, a meta material is an artificial material, so you're not going to find this in nature. It's not naturally occurring, and it's a material that has electromagnetic properties that other materials in nature do not have, which can include stuff like redirecting electromagnetic waves in a way that just doesn't occur in nature, and that can even include light. So in the nineteen sixties there was this scientist named Victor Veselogue who hypothesized way back in sixty eight that it should be possible to have a material that could have a negative refractive index. Okay, wait, what does that mean? All right, So again, remember we talked about this earlier with refraction. When light passes from one medium into another medium, the path of that light will change because light traveling through the air and then hitting the water will change because the speed of light itself changes as it goes from medium to medium. So that we all understand, and again that's due to the differences in the refractive indices of these two medium air has wa refractive index essentially one, and clear water would have another like one point three three. The bigger the difference between these two indices, the more dramatic the angle is going to be. And in the natural world, we would describe all these indices as having a positive value. But what would happen if you created a material that had a negative refractive index, so that the light bent in a different way, like it bent at a negative angle as opposed to a positive angle. Thes A lago suggested that such a material is entirely possible without violating the laws of physics, which is a good thing because violating those kinds of laws will really get into heaps of trouble. But more seriously, admit that while such materials don't exist in nature, it should be possible to create that kind of material, or at least the material itself does not go against the rules of the universe, even if we never figured out how to make the darned stuff. As a Lagos said, such material would behave oddly when exposed to electromagnetic waves, at least waves at specific frequencies. Because it would probably be impossible to make a material that could interact across the entire electro magnetic spectrum in a specific way. You could do it in chunks of the electro agnetic spectrum, because again that spectrum covers a huge range of wavelengths. So the materials, composite parts, the cells that make up this material would determine which frequencies in the electromagnetic spectrum would behave differently when interacting with this stuff, and specifically those materials, those cells, those components would have to be the same size or smaller than the wavelengths you were looking to manipulate. So as you get further into the electromagnetic spectrum, those components have to get tinier and tinier. You get down to the microscopic level, and then you blow that out of the water and you get even smaller, because if you want to get down to the visible spectrum, you have to be at the nanoscale. A nanometer is one billionth of a meter and at that scale things get wacky. As for what you would make this material out of, well, that could be conventional stuff. It wouldn't have to be anything true the exotic. The material itself could be made up of metals or plastics, all sorts of stuff. The important part would be the various cells would be the correct size, orientation, shape, et cetera, in order to achieve whatever goal you set out to make. So that's what would affect the electromagnetic waves in different ways more than the material itself. It's interesting because we often think of creating specific effects by going with a particular chemical composition of materials. Right, Like copper is a very good electric conductor, for example, so we often think of copper in the term in terms of things like wiring. There are other materials that are actually better conductors than copper, but they also get more rare and more expensive, so copper was kind of what we went with. Well, what Vesi Lago is saying is that we wouldn't so much be considered in the atomic nature of the material as opposed to the physical structure of that material, like how small or how large it is, what shape it is, and how it is arranged geometrically, and what or what's orientation is with respect to the incoming electromagnetic radiation. That's what's important, the physical actual arrangement of this material, which is really interesting way of thinking about things. Now, remember the Doppler effect that I mentioned earlier. Vezi Lago said that with the right negative refractive index, a material could produce a reverse Doppler shift. That's crazy, right, So let's say that you had a stealth plane that was coded with this kind of stuff, and instead of trying to absorb or redirect radar uh energy like the electromagetic waves that a is being sent out by radar. Instead, what's doing is reversing the Doppler shift. So that way, if this plane were approaching you, the reading you would get would indicate to you that, oh, there is an object there, but it's moving away, Whereas if the plane we're flying away, you'd look at and say, oh, there's an object that's coming toward us, because the dopplership would be reversed. This is hard for me to wrap my head around the idea that this material would interact with electromagnetic radiation in such a way as to create a result that's counterintuitive. It doesn't go the same way as what we're used to because again, this material doesn't appear in nature. If it did, then we wouldn't find it counterintuitive at all. We just say like, oh, that's this material as opposed to that material. But because it doesn't appear in nature, we don't really think about this stuff. We don't encounter it really interesting. However, now, when vessel Lago said all this, it was all purely in the hypothetical realm. He said, there's no reason why this could not exist, but we didn't have a way of making it. Things are different now. Starting around the early two thousand's, scientists started to experiment in trying to create meta materials, and in fact we're starting to be successful, specifically for things like in the microwave range of electromagnetic radiation, so that scientists were able to create a cloaking device for the microwave range, where they were able to put a little cylinder in the path of a microwave beam and use this meta material stuff to redirect the microwaves so that the microwaves passed around the cylinder and continued on as if nothing were there. So to the microwave detector, there was nothing in its path. Fascinating, but again, doesn't work for the visible light spectrum. Right if we were to look, we'd see, okay, the cylinders still there, because the cloaking device only effects radiation in the microwave range of wavelengths. So to get the visible light version of this, we have to reduce the size of all those components within the meta materials, because microwaves are small, but they're not in the nanoscale small like the visible light spectrum is the other side of that. Is kind of like when I was talking with chromatic aberration earlier. Visible light spectrum that's made up of a range of wavelengths. Right, the red wavelengths are longer than the violet wavelengths are on the other side of the spectrum. So it's hard to find materials and a size and orientation that will work with the entire range of visible light, which means it's hard to create a cloaking device that can work for all light as opposed to just part of the spectrum. So even if we get everything down to the correct size, we might find it difficult to cloak stuff effectively across the entire visible action, which might mean that we just end up with very oddly colored stuff. Also, we have to remember that when you get down to the nano scale, things behave differently like the stuff that we're used to at the macro scale at the classic scale of physics start to break down when you get down to the nano scale. For example, gold gold is gold, right like when you look at gold, it's a gold color. It's shiny, yellowish gold color. When you break down gold down to nanoparticles, It actually, depending on its size, will start to reflect light at different wavelengths. So you can have gold particles that look red or gold particles that look blue, which is weird to say, like, yes, it's gold, but it's red. Now, you you're kind of confusing me because we've used the same word to describe both the color and the material itself. It's like an orange, right, if an orange were purple, but we still call it it an orange. It probably wrinkle your brain a little bit, or at least the wrinkles my brain. I mean, I'm a simple person, so that's why it gets to me. But the idea of like, at the nano scale, gold could be red or blue is weird. It also means that when we started getting down there, it may mean, yeah, we figured out the the right size and the right orientation for all these particles to redirect light. However, once we get the elements down to the nano scale, there are other properties that emerge that we did not anticipate, and that's going to make it even more difficult. So there are lots of challenges here. More than that, we may just find that we cannot create a practical cloaking device that works across the visible spectrum um ever, at least not anything that will work better than within specific narrow use cases. There have been some demonstrations that in uh conditions where there's some light scattering effects, that you can actually have a really effective cloaking device, but that requires other things to be in place, like fog or missed that when you have something that's causing light to scatter, it becomes easier to redirect certain light and make it difficult to see something. You can effectively have an invisible object in the space, but then you're also talking about these other things that are impacting that You're already impacting visibility at that point anyway, So it's got very limited utility. Still really fascinating, and I'm not saying we're never going to get there. I would never say that, because people way way smarter than I am or working on these kinds of technologies. Whether there's ever a practical use for it, that's another question, because while you might be able to create something that is invisible to the naked eye, you would still end up having to factor in things like radio waves, microwaves, all sorts of stuff, because again, not all wavelengths are the same, and if it cannot manipulate or warp these these incoming electromagnetic waves equally across the spectrum, then it's going to be detectable by something. And also you have to still fix that issue that if you don't have a way of allowing at least some of that light to pass into the cloaked area, it will be pitch black inside the cloak because no light is coming in. It's all being redirected around it. There are other elements that you have to worry about. Two. I didn't even get into things like phase shifting, largely because I only have a limited understanding of it, and I quickly get out of my element. And while I could attempt to try and go down road, I would probably steer us all the wrong way, and then I'd get a lot of messages calling me out on that. And rightfully so, even as it stands, I worry that I've oversimplified things to a point where I'm being misleading. It is difficult to break this down to a level that I am comfortable communicating without feeling like, oh, I'm just saying things, but I don't understand what I'm talking about and that really comes down to the fact that I haven't taken a science class in why like almost thirty years, so I'm working on a lot of old brain cells that are are grumpy that I've called on them for this episode. Still fascinating stuff. And the demonstrations I have seen even of the limited quote unquote invisibility where it's not the visible spectrum but it's other ranges of the electromagnic spectrum, They're amazing. And the idea that we can create materials that have counterintuitive reactions to electromagnetic radiation is incredibly fascinating. And there are some really cool applications beyond the fantasy science fiction concept of invisibility, like completely transforming optics, so that you could have, at least on one level, a much simpler approach to optics where you have incredible effects, but you've really reduced the complexity of the overall material, the overall UH tool, for example, like a telescope, and you were able to do that by using specific meta materials like that, to me is truly amazing stuff. Being able to reduce complexity and points of failure by engineering material that just more effectively redirects or interacts with electromagnetic radiation. That's mind blowing. Like to me, that is science fiction, and yet it's stuff that's unfolding right now, and that's why I think it is so cool. All Right, I'm done geeking out about invisibility now, not really done, but I'm done talking about it. So if you have suggestions for topics I should cover. I've got a planned episode coming up where we're gonna talk about the history of spy balloons because obviously that's been in the news a lot lately, so I want to talk about that because that history stretches way back, y'all, and I want to talk about like the early use and then the the evolution of the technology and the use of such balloons and look forward to that in the near future. If you have other topics you would like me to tackle, let me know. You can reach out on Twitter. The handle for the show is tech Stuff hs W, or you can download the I Heart radio app. It's breed to download and use. You can navigate over to tech Stuff by putting that into the little search field. It will take your right to the page. You'll see there's a little microphone icon there. Click on that you can leave a voice message up to thirty seconds in length. Let me know what you'd like to hear in the future, and I'll talk to you again really soon. Yeah. Text Stuff is an I Heart Radio production. For more podcasts from my Heart Radio, visit the i Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.

Welcome to Tech Stuff, a production from I Heart Radio. Hey there, and welcome to tech Stuff. I'm your host, Jonathan Strickland. I'm an executive producer with I Heart Radio and how the tech are you? All right? I'm gonna start this episode with a rant that arguably is almost moot at this point and is certainly tangion shoaled to the episode, But it has to do with bookstores and how they classify types of books. Now, if you've ever been in a bookstore, like a brick and mortar bookstore, and then you've looked around at the various categories like mystery, history, romance, all that sort of stuff, chances are at some point you encountered a section that was called something like science fiction and fantasy, and you would have your swords all mixed up with your lasers. In a quick shout out to the podcast Sword and Laser, which is pretty dark and great. Ut I've always been kind of grouchy about this. I felt that while science fiction and fantasy both fall into the realm of speculative fiction, they aren't the only ones. I mean a lot of horror falls into that as well, But horror doesn't tend to be grouped with science fiction and fantasy. And of course psychological horror might not fit into speculative fiction, like a person going on some sort of rampage or something, but the kind of horror where a fear feeding alien who looks like a clown definitely falls into that category. But still horror gets its own section. So why not science fiction and fantasy? And I guess I'm touchy about this because my parents are authors. Dad in particular has written a lot of science fiction, fantasy, and horror novels, as well as mystery novels and also young adult novel You know what, Dad's written a lot of stuff, and I just thought it's weird that his science fiction books and fantasy books would appear side by side in the same section. In fact, his agent and publishers were so concerned about this that at one point he had to write under a pen name for a science fiction book so that it wouldn't be right next to his fantasy books. Now, none of that really matters for this episode, except there is an element that can be found both in fantasy books and science fiction books as well as other media that I'm going to talk about today, and that's stuff. What turns you invisible. Now, in fantasy, it might be an actual cloak, so you really have a cloaking an invisibility cloak. It might be a ring that at some point you can't have to chuck into a volcano. It might be a spell or a potion, whereas in science fiction it might be some sort of technology that's incorporated in say a spaceship, that allows it to pass undetected as it sneaks up on an enemy or encounters an alien world. Now, I thought we might talk a bit about tech intended to grant invisibility in the real world. We've got some real world examples of stuff that does this to a certain degree, though spoiler alert, we do not have a technology that can cover the entire visual spectrum of light that would work like an invisibility cloak or something. There are folks working on it, but we're definitely not there yet. However, we do have some really interesting examples that at least brush up against invisibility that we'll talk about. Now, before we dive into the various technologies, let's talk about how vision works and chat a bit about light. So, way back in the day, smarty pans philosopher types tried to suss out what is light and how does vision work. Pythagoras had the angle on some stuff, but when it came to how vision works, he ended up being a bit obtuse. Yes, I'm gonna throw in lots of puns and dad jokes. Anyway, Pythagoras thought that vision worked because we were effectively shooting out rays of vision with our eyeballs, like vision was something that came from us, extended out into the world and effectively lit the world around us with vision, and so these vision rays would go out and hit objects, which let us see them. So we were kind of like Superman with this heat vision, except we're just constantly shooting out this sort of light. And you might think, silly Pathagoras, wouldn't that mean we could all see in the dark. But maybe what he was saying is that, you know, some of this light that is invisible to us in the world, like we can't see it shooting out of everybody else's eyes, but the it's what comes out of our eyes and hit stuff that's already lit, and that's what lets us see it. And so he was just thinking it was an innate ability within the human eye and presumably animal eye as well. Epicurus had a totally different take on it. The philosopher known for emphasizing the pursuit of a happy life through eliminating fear and pain, which sounds nice, felt that objects themselves were emitting this light, that they were emitting this visible ray that our eyes could detect. So our eyes are detectors, but the objects themselves are emitting this, and that as a result, we could see light coming from the objects. Again, this doesn't really hold up when you're wandering around your house in the dark and you bark your ship on a coffee table. But what he was saying was that, all right, you're in a well lit area. Every single object that has this thing in it allows you to see it because it's emanating this energy that your eyes can detect. So a little closer to being correct than Pythagoras, but still missing stuff. Now you also had philosophers who started to get a little closer to what we know to be the truth that light can reflect off surfaces, bouncing off of them, or that it can pass through certain types of material like glass or water. But when it does, when light travels from that and hits something like the surface of glass or the surface of water, it bends, the light changes direction. Now these observations gradually lead to later smarty pants folks crafting lenses intended to bend light in specific ways. Not just you know it, not just it bends light, but I want to bend light so that it goes to this specific point. And an Arabic polymath in what is today known as Iraq even al hythem I figured that the human eye was doing the same sort of thing as a surface of glass or water. That light when it goes into the human eye would end up being directed. And also that light when it's going out in the world, it's bouncing off of objects, and it's the light bouncing off those objects that passes through the human eye against bent in a way where we can perceive it, and thus that's how vision works. This was around one thousand CE, or a d if you're using the more common nomenclature. Now. By the early seventeen hundreds we had Isaac Newton proposing that light was made of little corpuscles, little particles. In other words, that light really was made up of some tiny, tiny, tiny little piece of something. And it made some sense because light travels in a straight line, and it bounces off objects, just as a physical particle would do. Like if you had a tennis ball, then you threw it at a wall, it would bounce off the wall, and depending on the angle you threw the ball at and then that it hits the wall at, it's going to bounce in a specific way. Well, what Newton was saying, light appears to be doing the same thing. So it must be made of lots of tiny little tennis balls, although he didn't say tennis balls, but you know, just to continue the analogy. Others, however, would describe light as behaving like a wave, like a sound wave. And as it would turn out, both explanations were kind of right. Light behaves as a wave and a particle, but we wouldn't be sure about that for you know, a couple hundred years. But thinking about light as either a particle or a wave helps us understand what it's doing when it encounters other stuff. So let's start by thinking of as a ray of particles, and it's a ray that travels in a straight line until it encounters something else. And let's talk about how light interacts with stuff. So first up, as reflection, This is when light bounces off of a surface like a mirror or a tree where you our face. So light will bounce off a smooth surface at an angle equal to the angle of the incoming ray, making with the surface like there's a thing called the angle of incidents, and so you can predict what that angle is going to be if you're working with a perfectly smooth surface. This is what we call the law of reflection. However, we don't have perfectly smooth surfaces. If we did, then yes, you would see light bend in this way or reflect off in this way every single time. But we don't have perfectly smooth surfaces. Instead, we've got surfaces that have imperfections. And because of this, and because the wavelengths of light are very very very small, light will bounce off at all sorts of angles because again not perfectly smooth. This is why something like a tabletop won't disappear if you change your angle of view, right like if it if the light bounced in a very specific way because you had a perfectly smooth table, well that would mean that if you moved out of the angle of incidents, you would no longer see the tabletop because there will be no light bouncing off of it that you could see, which is kind of weird to think about, like the idea that something exists in one perspective, but at another it seems to not exist anymore. It does, you just can't see it. There are other reasons why it's gonna be don't have perfectly smooth tabletops. The big one being that if you had a perfectly smooth tabletop, there will be no friction. If you said anything on the surface of the tabletopic could slide all over the place. But we'll leave that beat. But then you've got absorption. Okay, so stuff can absorb light. Now, I'm sure you all know about the spectrum of light. We're gonna be talking about a lot in this episode. That's the old roy g biv red, orange, yellow, green, blue, indigo, and violet. That's the order that you would see if you were to see a rainbow. Well, that happens to be the spectrum of visible light. It's going from the longest wavelength red to the shortest violet. But we're gonna talk more about wavelengths in a little bit, and a lot of matter can absorb certain wavelengths of light. That means those wavelengths do not get reflected back at you when the light hits that object. For example, chromium, the stuff and rubies that makes them red, absorbs the green and blue wavelengths of light, so the only stuff that's getting reflected back is in the red wavelengths of light. So rubies appear red to us because the other wavelengths of light have been absorbed by the gem. If you had something that could absorb all wavelengths of light, it would look black, like pure black, as if there were avoid rather than you know, whatever the thing is. And there are special paints out there that absorbed nearly all visible light hitting them, and seeing stuff covered in that paint is trippy because it looks like there's just a a thing shaped void in a physical space. So one example I've seen as an apple that's been half painted uh with this special super uber black paint, and you put the apple on a little rotating pedestal, and what you'll see is that when the apple rotates so that the red of the apple starts to give way to the void black, it looks like half the apple is missing, but you're not seeing the inside of the apple. It's just the half the apple is just a black shape, and if it turns all the way around, it's like the apple doesn't exist anymore. You just see a black field in the shape of an apple. It's crazy. You could do that with a pumpkin and you would have a pumpkin shaped hole instead of a jack ol Internet Halloween, which would be super awesome in the daytime, wouldn't be so effective at night. But it is really neat stuff. By the way, there are different types of this ultra black paint out there. There's one kind that was heavily trademarked, and then someone else went and developed a similar kind, specifically because they felt it was wrong for someone to try and trademark a color. But yeah, that's that's a topic for another episode. Then we have when light goes from one transparent medium to another, when it passes through a barrier, and then what happens to it. So this would be like when light travels through air, hits the surface of water or air, and it hits a lens. That's when you get refraction. Now I'll explain what refraction is because it's very important for our discussion. But first let's take a quick break. Okay, Before the break, I was talking about refraction. Refraction is when light does pass from one medium to another and it changes speed. Now that might sound weird because everyone knows light is the fastest stuff in the universe. It is the speed limit of the universe. There is nothing faster than light. In fact, we use the speed of light as a constant. The famous equation E equals mc squared is referencing the speed of light. That's energy equals the mass of something times the square of the speed of light. So if it is a constant, how can the speed of light change? Those two things don't make sense. Well, when we talk about the speed of light as a constant, we're referring to light traveling through a vacuum, an empty medium, outer space, outer space where you've got a true vacuum. But when light hits a medium like say an atmosphere or water, or the lens of a telescope or glasses, it does slow down a little. It changes speed. It can't get faster than it can through the vacuum of space. That's the as fast as anything can go. But if it hits something like trans transparent medium, it will change speed. It slows down. Think of it kind of like walking in just the open air, like you're going out for a stroll, versus trying to walk in a swimming pool. You know, when you're in a swing pool and you're trying to walk across the pool, you feel the resistance of all that water that slows you down, Whereas when you're walking through just you know, the room, then all you're doing is walking through air. You have much less resistance and you're able to go much more quickly. It's very similar to that. So when light changes speed as it passes into a new medium, it bends. The amount of bending or angle of refraction depends upon how much slower the light will travel as it moves through the new medium. In fact, we call this the refraction index when we look at the different transparent media and we say all right, well, based upon this difference, will know how much of a bend will see in the light. So if you've ever seen like a shaft of light shining down to a a surface of water, then you're looking at like a cross section, like you can see both above and below the water. You actually see where the bend is there. Or if you want to do a really easy one, you get a glass you fill it up with water, like maybe to the halfway point. Put a straw on that glass, and then you look at the glass from the side, and you'll see that the straw appears to bend at the point where it crosses over into the water. That's because of this refraction and this refractive index and the difference between the two, and we get that that little bend there. So a lens is shaped in such a way as to bend light to a specific focal point. If we're thinking of it in the terms of rays, right, array coming in at the edge of the lens, where it is more narrow, is going to be bent a certain way. Array coming in through the center of the lens is going to go in a certain direction. And then at the very bottom of the lens, which is again perhaps more narrow we're looking at our typical lens, would then be bent in a certain way so that these these different bent rays of light will converge at a point where we can get, say, an image. This is how we create things like corrective lenses for glasses, and bending light is really the secret sauce. In most invisibility technologies or cloaking technologies. This is pretty easy to understand. There's another way to look at this, by the way, and in fact, I would argue the other way to look at it makes it even easier to understand, which is to think of the incoming light as waves and think of the lens like let's say that we've got our our regular convex lens where it's narrower at the top and bottom and thickest in the middle. Right, the wave hitting the top and the bottom, those waves are going to be slowed down less than the wave that's hinting hitting the center of that lens, because the the material is thinner at the top and bottom and thicker in the middle. So the waves at the top and bottom slow down a little bit, but not a lot. The wave in the middle slows down the most. And what you get on the other side of the lens is this converging wave, being the wave is starting to get uh smaller and smaller to a focused point because of the the speed at which it has traveled through that lens, and it converges, and that's where you get your your focal point. That's another way to think about it. It becomes really important when we start talking about invisibility technologies. All right, something else we have to know about light. It's part of the electro magnetic spectrum. As I'm sure you're all know, the visible of lights just one tiny part of of a band of frequencies that make up what we call light like light that we can see. That's one tiny slice of light. Overall. There's also infrared light, which is on one side of the visible spectrum, an ultraviolet light, which is on the opposite side. We cannot see infrared and ultra violet directly. We can create technologies that let us detect this kind of light and then see it in the sense of converting that into light that we can actually directly perceive. Right, So, if you have infrared goggles, you're not actually looking at infrared light. What you're looking at is a interpretation of infrared that's been fed into technology that gives you light that you can actually see, so that things that are really hot appear red, and things that are cooler might appear blue, that sort of stuff. But the red and blue, that's red and blue. That's not infrared. It's just it's been interpreted through the technology. However, you took the the goggles off entirely, you wouldn't be able to see anything because everything would be dark. That kind of thing. It's night vision goggles work on a similar idea. So that's where light fits. But then beyond light, you've got all sorts of different types of electro magnetism, Like you have different flavors of it if you would, like you've got radio waves that's on the the longest wavelength side of the electromagnetic spectrum, and then on the opposite side, on the shortest wavelength side, you have gamma radiation. So what determines the nature of this electromagnetism, what determines what it can do and what we can use it for, is its wavelength or its frequency. The two are related. The longer the wavelength, the lower the frequency. The shorter the wavelength, the higher the frequency. But here's the thing. All of these frequencies are traveling at the same eat. That electromagnetic speed is the speed of light, so they're all traveling at the same speed. It's just that they have different lengths of of waves, right. So radio waves are very very very long, gamma waves are very very very short. They both travel at the speed of light. But it means that the number of waves that pass you in a given second are very different for radio than it is for gamma, because more of the gamma can pass you in the second than the radio waves because the length is so much shorter. Well, since visible light occupies a range of frequencies, we can encounter some challenges when we start to think about ways to manipulate light. So there's this effect called chromatic aberration. Sometimes it's called chromatic distortion, which be a great name for a band. Maybe you just cover social distortion songs. Anyway, Chromatic distortion occurs because visible light is made up of a band of wave wavelengths of light. You know, red has the longest wavelengths invisible light, Violet has the shortest wavelengths, and when light hits a refractive surface like a lens, not all these wavelengths are going to bend at quite the same angle. So you might notice that some parts of an image have little borders or fringes of color around them. And that's because that wavelength of light, let's say it's red, bent at a slightly different angle from the other wavelengths, and so you get this kind of halo effect. Now, the reason I bring this up is that one of the biggest challenges when it comes to creating invisibility technology is that the methods we might use could work differently with some parts of the visible light spectrum from others, and you might end up with the technology that can redirect certain parts of the visible spectrum in a specific way, but not all of the visible spectrum. And that would mean that you would still be able to see the cloak or the cloaked object, but it would look kind of funny because you wouldn't see all the colors you normally would, or it would appear to be a different color than what it quote unquote really is. If you want to think about another way, imagine that you've got a gap that's just wide enough to let visible light from green to violet go through. So anything that's green to violet and the visible spectrum can pass through this tiny little gap. But that would mean that wavelengths that were in red, orange, and yellow light because of roy g BIV, those wavelengths would bounce off because the gap is too small for these wavelengths to pass through it. It's it's too narrow. That's kind of what I'm going with here, all right, So when we come back, we're going to talk about some of the technology is meant to make something invisible, and we're gonna start with stealth technology after we take this quick break. All right. I'm I'm a kid of the seventies and eights, and I remember when the stealth bomber was becoming big news. It was such a cool science fiction technology. We had heard about things like cloaking devices and stuff, but here was a plane that could at least what we were told passed invisibly for radar systems. So clearly stealth technology, like the famous stealth bomber, you know, is not invisible to the naked eye. We can see it. It's not like it's Wonder Woman's invisible jet here. So we're talking about a vehicle that won't show up on radar, but we can still see it. That's because radar is operating in a different band of frequencies in the electromagnetic spectrum then visible light. Right, So if there's something in a direction, you've got a radar emitter. The radar emitter is shooting out electromagnetic waves, and if that something is there, some of those waves are going to hit that something and bounce back. So if in addition to the emitter. You have a detector that can detect the echoes of these electromagnetic waves you've sent out, then you know, hey, there's something there, right, And if you actually measure the difference in time it took for the waves to go out and then bounce back, you know how far away it is because you know how fast those electromagnetic waves are traveling. So you measure the amount of time it took for the waves to go out and bounce back, that tells you how far away the object is. You also can figure out whether or not the object is moving towards you or moving away from you because of the old Doppler effect. So if the object is moving away from you, the returning waves will actually be longer than what you sent out toward it. If it is moving towards you, then the returning waves are going to be shorter than what you sent out, and the amount of elongation or shortening would tell you how quickly this thing is traveling. So it's really interesting, like that's that Doppler effect also very important to what we're going to talk about in just a bit. So let's say that you wanted to create an aircraft that could go undetected by radar. What do you do well, You probably use a combination of strategies. So you might use some materials that can absorb electromagnetic waves in the frequencies that are being used by radar, so that way, when the wave hits the aircraft, the aircraft absorbs that energy and there's not enough to echo back to the detector, so it just it just gets swallowed up. This would be kind of that super black paint we were talking about earlier, where it absorbs most of the visible light. In this case, it would be absorbing the radar electromagnetic energy. But you probably all start going to play a bit with reflection, and you do this by designing your aircraft's exterior with these funky angles on them, so that if a radar beam does hit the aircraft, it gets reflected in an odd direction because of that angle that it hits. You know, the angle of incidents where the wave hits the aircraft means that it's going to get reflected off in a direction where hopefully there's no detector, so no one can see that there's an aircraft there. This combination of strategies makes it very difficult for radar stations to detect stealth aircraft, though again the aircraft itself itself is still totally visible to us because it's not redirecting or absorbing visible light. It's doing it in say the microwave range. Over time, as scientists develop new approaches to manipulating, absorbing, and reflecting electromagnetic radiation, we would find ways to make objects quote unquote invisible to specific kinds of electromagnetic frequencies. But it's a very different thing to make an object undetectable from say a microwave a mitter, than it is for visible light. Now, imagine for a moment that you could redirect light around an object, so the light would curve around an object, move around to the other side, and then continue on as if there were no object for the light to interact with at all. So it's not passing through whatever is cloaked, it's just going around whatever is quoaked and then getting back on track. Then an outside observer would not see anything there, right, They just look and it would just look like empty space. You'd be looking at everything that's on the other side of the object from your point of view, and that would be it. That would be really cool. Also would be very tricky because if you're making all the light curve around the object, and I'm saying all the light that's coming curves around it, that means inside you wouldn't be able to see anything. It would be perfectly dark because all light that's coming to you has been redirected. So let's say that it's like a small structure and you're inside it. It would be completely dark inside that structure because all the incoming light has been redirected. You could potentially light something inside the structure and thus be able to see And if the structure is not allowing light to pass back out, then you'd be able to see inside, but you wouldn't be able to see the outside world. Nothing in the outside world would be visible to you because all that light has been redirected. You would have to have a way to allow some of the light from the exterior world to come through, but still pass enough of the light around so that an outside observer would be unaware there was something there. That's super duper tricky. It's one of the hardest parts of the cloaking device, one of not the only so wicked hard to do. As it turns out, now we've seen some fun approaches this kind of a thing that that do succeed in certain frequencies like the microwave range. Uh. And we've also seen some fun ways to simulate a cloaking device, but it's not actually a cloaking device. For example, a fun one I have seen is a screen mounted on say the side of a truck, like like a semi truck or something along those lines, And you've got a screen on one side of display, and on the opposite side of the truck you have cameras mounted to capture a live feed of whatever is on the other side of the truck, and then it feeds that live feed to the screen that's mounted on the side, So the truck is totally solid. Light is not passing through it or going around it. Instead, you're just looking at a video feed on whatever is the other side displayed on the truck ruck. And I've seen this sort of thing at various events where it's just kind of fun, like you can actually see people walking on the opposite side of the truck, but it's because they're being displayed on this screen. It's not that the truck is actually transparent or has magically disappeared, and it's a fun effect, or it can be, but it's very limited and you know exactly what's happening, right, It's not like it's mysterious. Now. I have seen this incorporated into costumes in a way that was kind of fun. I saw a guy in a zombie costume once where he had mounted a tablet inside his costume in the front, and he was had a camera mounted on his back and it was feeding live video from the camera on the back to the tablet so that it looked like there was a hole in his torso. Like his torso just said this fist shaped hole all the way through, and that you can see video from the opposite side feeding through on the tablet, which was effective if you're looking at him at on. If you're looking at them from an angle, it didn't work so well, but it was a really clever use of this particular approach. Still not really a cloaking device. Right. To get into the possibility of actually bending light around an object, we have to talk about some really advanced technology, and I'm talking about stuff like meta materials and nanotechnology. So first up is meta material. What the heck is a meta material? I've never met a material I didn't like, No. Essentially, a meta material is an artificial material, so you're not going to find this in nature. It's not naturally occurring, and it's a material that has electromagnetic properties that other materials in nature do not have, which can include stuff like redirecting electromagnetic waves in a way that just doesn't occur in nature, and that can even include light. So in the nineteen sixties there was this scientist named Victor Veselogue who hypothesized way back in sixty eight that it should be possible to have a material that could have a negative refractive index. Okay, wait, what does that mean? All right, So again, remember we talked about this earlier with refraction. When light passes from one medium into another medium, the path of that light will change because light traveling through the air and then hitting the water will change because the speed of light itself changes as it goes from medium to medium. So that we all understand, and again that's due to the differences in the refractive indices of these two medium air has wa refractive index essentially one, and clear water would have another like one point three three. The bigger the difference between these two indices, the more dramatic the angle is going to be. And in the natural world, we would describe all these indices as having a positive value. But what would happen if you created a material that had a negative refractive index, so that the light bent in a different way, like it bent at a negative angle as opposed to a positive angle. Thes A lago suggested that such a material is entirely possible without violating the laws of physics, which is a good thing because violating those kinds of laws will really get into heaps of trouble. But more seriously, admit that while such materials don't exist in nature, it should be possible to create that kind of material, or at least the material itself does not go against the rules of the universe, even if we never figured out how to make the darned stuff. As a Lagos said, such material would behave oddly when exposed to electromagnetic waves, at least waves at specific frequencies. Because it would probably be impossible to make a material that could interact across the entire electro magnetic spectrum in a specific way. You could do it in chunks of the electro agnetic spectrum, because again that spectrum covers a huge range of wavelengths. So the materials, composite parts, the cells that make up this material would determine which frequencies in the electromagnetic spectrum would behave differently when interacting with this stuff, and specifically those materials, those cells, those components would have to be the same size or smaller than the wavelengths you were looking to manipulate. So as you get further into the electromagnetic spectrum, those components have to get tinier and tinier. You get down to the microscopic level, and then you blow that out of the water and you get even smaller, because if you want to get down to the visible spectrum, you have to be at the nanoscale. A nanometer is one billionth of a meter and at that scale things get wacky. As for what you would make this material out of, well, that could be conventional stuff. It wouldn't have to be anything true the exotic. The material itself could be made up of metals or plastics, all sorts of stuff. The important part would be the various cells would be the correct size, orientation, shape, et cetera, in order to achieve whatever goal you set out to make. So that's what would affect the electromagnetic waves in different ways more than the material itself. It's interesting because we often think of creating specific effects by going with a particular chemical composition of materials. Right, Like copper is a very good electric conductor, for example, so we often think of copper in the term in terms of things like wiring. There are other materials that are actually better conductors than copper, but they also get more rare and more expensive, so copper was kind of what we went with. Well, what Vesi Lago is saying is that we wouldn't so much be considered in the atomic nature of the material as opposed to the physical structure of that material, like how small or how large it is, what shape it is, and how it is arranged geometrically, and what or what's orientation is with respect to the incoming electromagnetic radiation. That's what's important, the physical actual arrangement of this material, which is really interesting way of thinking about things. Now, remember the Doppler effect that I mentioned earlier. Vezi Lago said that with the right negative refractive index, a material could produce a reverse Doppler shift. That's crazy, right, So let's say that you had a stealth plane that was coded with this kind of stuff, and instead of trying to absorb or redirect radar uh energy like the electromagetic waves that a is being sent out by radar. Instead, what's doing is reversing the Doppler shift. So that way, if this plane were approaching you, the reading you would get would indicate to you that, oh, there is an object there, but it's moving away, Whereas if the plane we're flying away, you'd look at and say, oh, there's an object that's coming toward us, because the dopplership would be reversed. This is hard for me to wrap my head around the idea that this material would interact with electromagnetic radiation in such a way as to create a result that's counterintuitive. It doesn't go the same way as what we're used to because again, this material doesn't appear in nature. If it did, then we wouldn't find it counterintuitive at all. We just say like, oh, that's this material as opposed to that material. But because it doesn't appear in nature, we don't really think about this stuff. We don't encounter it really interesting. However, now, when vessel Lago said all this, it was all purely in the hypothetical realm. He said, there's no reason why this could not exist, but we didn't have a way of making it. Things are different now. Starting around the early two thousand's, scientists started to experiment in trying to create meta materials, and in fact we're starting to be successful, specifically for things like in the microwave range of electromagnetic radiation, so that scientists were able to create a cloaking device for the microwave range, where they were able to put a little cylinder in the path of a microwave beam and use this meta material stuff to redirect the microwaves so that the microwaves passed around the cylinder and continued on as if nothing were there. So to the microwave detector, there was nothing in its path. Fascinating, but again, doesn't work for the visible light spectrum. Right if we were to look, we'd see, okay, the cylinders still there, because the cloaking device only effects radiation in the microwave range of wavelengths. So to get the visible light version of this, we have to reduce the size of all those components within the meta materials, because microwaves are small, but they're not in the nanoscale small like the visible light spectrum is the other side of that. Is kind of like when I was talking with chromatic aberration earlier. Visible light spectrum that's made up of a range of wavelengths. Right, the red wavelengths are longer than the violet wavelengths are on the other side of the spectrum. So it's hard to find materials and a size and orientation that will work with the entire range of visible light, which means it's hard to create a cloaking device that can work for all light as opposed to just part of the spectrum. So even if we get everything down to the correct size, we might find it difficult to cloak stuff effectively across the entire visible action, which might mean that we just end up with very oddly colored stuff. Also, we have to remember that when you get down to the nano scale, things behave differently like the stuff that we're used to at the macro scale at the classic scale of physics start to break down when you get down to the nano scale. For example, gold gold is gold, right like when you look at gold, it's a gold color. It's shiny, yellowish gold color. When you break down gold down to nanoparticles, It actually, depending on its size, will start to reflect light at different wavelengths. So you can have gold particles that look red or gold particles that look blue, which is weird to say, like, yes, it's gold, but it's red. Now, you you're kind of confusing me because we've used the same word to describe both the color and the material itself. It's like an orange, right, if an orange were purple, but we still call it it an orange. It probably wrinkle your brain a little bit, or at least the wrinkles my brain. I mean, I'm a simple person, so that's why it gets to me. But the idea of like, at the nano scale, gold could be red or blue is weird. It also means that when we started getting down there, it may mean, yeah, we figured out the the right size and the right orientation for all these particles to redirect light. However, once we get the elements down to the nano scale, there are other properties that emerge that we did not anticipate, and that's going to make it even more difficult. So there are lots of challenges here. More than that, we may just find that we cannot create a practical cloaking device that works across the visible spectrum um ever, at least not anything that will work better than within specific narrow use cases. There have been some demonstrations that in uh conditions where there's some light scattering effects, that you can actually have a really effective cloaking device, but that requires other things to be in place, like fog or missed that when you have something that's causing light to scatter, it becomes easier to redirect certain light and make it difficult to see something. You can effectively have an invisible object in the space, but then you're also talking about these other things that are impacting that You're already impacting visibility at that point anyway, So it's got very limited utility. Still really fascinating, and I'm not saying we're never going to get there. I would never say that, because people way way smarter than I am or working on these kinds of technologies. Whether there's ever a practical use for it, that's another question, because while you might be able to create something that is invisible to the naked eye, you would still end up having to factor in things like radio waves, microwaves, all sorts of stuff, because again, not all wavelengths are the same, and if it cannot manipulate or warp these these incoming electromagnetic waves equally across the spectrum, then it's going to be detectable by something. And also you have to still fix that issue that if you don't have a way of allowing at least some of that light to pass into the cloaked area, it will be pitch black inside the cloak because no light is coming in. It's all being redirected around it. There are other elements that you have to worry about. Two. I didn't even get into things like phase shifting, largely because I only have a limited understanding of it, and I quickly get out of my element. And while I could attempt to try and go down road, I would probably steer us all the wrong way, and then I'd get a lot of messages calling me out on that. And rightfully so, even as it stands, I worry that I've oversimplified things to a point where I'm being misleading. It is difficult to break this down to a level that I am comfortable communicating without feeling like, oh, I'm just saying things, but I don't understand what I'm talking about and that really comes down to the fact that I haven't taken a science class in why like almost thirty years, so I'm working on a lot of old brain cells that are are grumpy that I've called on them for this episode. Still fascinating stuff. And the demonstrations I have seen even of the limited quote unquote invisibility where it's not the visible spectrum but it's other ranges of the electromagnic spectrum, They're amazing. And the idea that we can create materials that have counterintuitive reactions to electromagnetic radiation is incredibly fascinating. And there are some really cool applications beyond the fantasy science fiction concept of invisibility, like completely transforming optics, so that you could have, at least on one level, a much simpler approach to optics where you have incredible effects, but you've really reduced the complexity of the overall material, the overall UH tool, for example, like a telescope, and you were able to do that by using specific meta materials like that, to me is truly amazing stuff. Being able to reduce complexity and points of failure by engineering material that just more effectively redirects or interacts with electromagnetic radiation. That's mind blowing. Like to me, that is science fiction, and yet it's stuff that's unfolding right now, and that's why I think it is so cool. All Right, I'm done geeking out about invisibility now, not really done, but I'm done talking about it. So if you have suggestions for topics I should cover. I've got a planned episode coming up where we're gonna talk about the history of spy balloons because obviously that's been in the news a lot lately, so I want to talk about that because that history stretches way back, y'all, and I want to talk about like the early use and then the the evolution of the technology and the use of such balloons and look forward to that in the near future. If you have other topics you would like me to tackle, let me know. You can reach out on Twitter. The handle for the show is tech Stuff hs W, or you can download the I Heart radio app. It's breed to download and use. You can navigate over to tech Stuff by putting that into the little search field. It will take your right to the page. You'll see there's a little microphone icon there. Click on that you can leave a voice message up to thirty seconds in length. Let me know what you'd like to hear in the future, and I'll talk to you again really soon. Yeah. Text Stuff is an I Heart Radio production. For more podcasts from my Heart Radio, visit the i Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.