WEBVTT - 100% Invisible 0:00:04.400 --> 0:00:07.800 Welcome to Tech Stuff, a production from I Heart Radio. 0:00:11.800 --> 0:00:14.760 Hey there, and welcome to tech Stuff. I'm your host, 0:00:14.920 --> 0:00:18.200 Jonathan Strickland. I'm an executive producer with I Heart Radio 0:00:18.440 --> 0:00:21.000 and how the tech are you? All right? I'm gonna 0:00:21.040 --> 0:00:26.440 start this episode with a rant that arguably is almost 0:00:26.480 --> 0:00:29.200 moot at this point and is certainly tangion shoaled to 0:00:29.240 --> 0:00:32.159 the episode, But it has to do with bookstores and 0:00:32.240 --> 0:00:36.279 how they classify types of books. Now, if you've ever 0:00:36.320 --> 0:00:39.120 been in a bookstore, like a brick and mortar bookstore, 0:00:39.240 --> 0:00:44.320 and then you've looked around at the various categories like mystery, history, romance, 0:00:44.320 --> 0:00:47.200 all that sort of stuff, chances are at some point 0:00:47.400 --> 0:00:50.320 you encountered a section that was called something like science 0:00:50.320 --> 0:00:54.040 fiction and fantasy, and you would have your swords all 0:00:54.120 --> 0:00:57.080 mixed up with your lasers. In a quick shout out 0:00:57.080 --> 0:00:59.160 to the podcast Sword and Laser, which is pretty dark 0:00:59.200 --> 0:01:02.520 and great. Ut I've always been kind of grouchy about this. 0:01:02.720 --> 0:01:05.440 I felt that while science fiction and fantasy both fall 0:01:06.000 --> 0:01:11.120 into the realm of speculative fiction, they aren't the only ones. 0:01:11.160 --> 0:01:14.240 I mean a lot of horror falls into that as well, 0:01:14.319 --> 0:01:16.880 But horror doesn't tend to be grouped with science fiction 0:01:16.920 --> 0:01:20.520 and fantasy. And of course psychological horror might not fit 0:01:20.560 --> 0:01:24.000 into speculative fiction, like a person going on some sort 0:01:24.040 --> 0:01:26.399 of rampage or something, but the kind of horror where 0:01:26.400 --> 0:01:29.440 a fear feeding alien who looks like a clown definitely 0:01:29.480 --> 0:01:33.639 falls into that category. But still horror gets its own section. 0:01:33.720 --> 0:01:36.240 So why not science fiction and fantasy? And I guess 0:01:36.280 --> 0:01:39.319 I'm touchy about this because my parents are authors. Dad 0:01:39.319 --> 0:01:42.200 in particular has written a lot of science fiction, fantasy, 0:01:42.240 --> 0:01:45.679 and horror novels, as well as mystery novels and also 0:01:45.760 --> 0:01:48.120 young adult novel You know what, Dad's written a lot 0:01:48.160 --> 0:01:51.680 of stuff, and I just thought it's weird that his 0:01:51.760 --> 0:01:54.320 science fiction books and fantasy books would appear side by 0:01:54.360 --> 0:01:58.080 side in the same section. In fact, his agent and 0:01:58.120 --> 0:02:01.639 publishers were so concerned about this that at one point 0:02:01.840 --> 0:02:04.280 he had to write under a pen name for a 0:02:04.360 --> 0:02:07.640 science fiction book so that it wouldn't be right next 0:02:07.720 --> 0:02:12.040 to his fantasy books. Now, none of that really matters 0:02:12.040 --> 0:02:15.520 for this episode, except there is an element that can 0:02:15.600 --> 0:02:19.640 be found both in fantasy books and science fiction books 0:02:19.880 --> 0:02:22.320 as well as other media that I'm going to talk 0:02:22.360 --> 0:02:26.600 about today, and that's stuff. What turns you invisible. Now, 0:02:26.639 --> 0:02:30.240 in fantasy, it might be an actual cloak, so you 0:02:30.320 --> 0:02:34.360 really have a cloaking an invisibility cloak. It might be 0:02:34.560 --> 0:02:36.600 a ring that at some point you can't have to 0:02:36.680 --> 0:02:39.400 chuck into a volcano. It might be a spell or 0:02:39.440 --> 0:02:43.440 a potion, whereas in science fiction it might be some 0:02:43.480 --> 0:02:47.480 sort of technology that's incorporated in say a spaceship, that 0:02:47.520 --> 0:02:50.040 allows it to pass undetected as it sneaks up on 0:02:50.120 --> 0:02:54.840 an enemy or encounters an alien world. Now, I thought 0:02:55.560 --> 0:02:59.560 we might talk a bit about tech intended to grant 0:03:00.080 --> 0:03:04.400 invisibility in the real world. We've got some real world 0:03:04.400 --> 0:03:07.120 examples of stuff that does this to a certain degree, 0:03:07.160 --> 0:03:11.000 though spoiler alert, we do not have a technology that 0:03:11.040 --> 0:03:14.560 can cover the entire visual spectrum of light that would 0:03:14.560 --> 0:03:18.760 work like an invisibility cloak or something. There are folks 0:03:18.800 --> 0:03:23.560 working on it, but we're definitely not there yet. However, 0:03:23.600 --> 0:03:26.960 we do have some really interesting examples that at least 0:03:27.000 --> 0:03:31.720 brush up against invisibility that we'll talk about. Now, before 0:03:31.760 --> 0:03:34.960 we dive into the various technologies, let's talk about how 0:03:35.400 --> 0:03:40.400 vision works and chat a bit about light. So, way 0:03:40.440 --> 0:03:44.040 back in the day, smarty pans philosopher types tried to 0:03:44.080 --> 0:03:48.720 suss out what is light and how does vision work. 0:03:49.360 --> 0:03:53.280 Pythagoras had the angle on some stuff, but when it 0:03:53.360 --> 0:03:55.360 came to how vision works, he ended up being a 0:03:55.360 --> 0:03:58.600 bit obtuse. Yes, I'm gonna throw in lots of puns 0:03:58.600 --> 0:04:02.960 and dad jokes. Anyway, Pythagoras thought that vision worked because 0:04:03.000 --> 0:04:07.800 we were effectively shooting out rays of vision with our eyeballs, 0:04:07.840 --> 0:04:11.400 like vision was something that came from us, extended out 0:04:11.440 --> 0:04:15.840 into the world and effectively lit the world around us 0:04:15.840 --> 0:04:19.480 with vision, and so these vision rays would go out 0:04:19.480 --> 0:04:23.080 and hit objects, which let us see them. So we 0:04:23.080 --> 0:04:26.839 were kind of like Superman with this heat vision, except 0:04:27.000 --> 0:04:31.800 we're just constantly shooting out this sort of light. And 0:04:31.880 --> 0:04:35.039 you might think, silly Pathagoras, wouldn't that mean we could 0:04:35.080 --> 0:04:37.440 all see in the dark. But maybe what he was 0:04:37.440 --> 0:04:39.400 saying is that, you know, some of this light that 0:04:39.560 --> 0:04:42.320 is invisible to us in the world, like we can't 0:04:42.400 --> 0:04:46.240 see it shooting out of everybody else's eyes, but the 0:04:46.640 --> 0:04:49.359 it's what comes out of our eyes and hit stuff 0:04:49.400 --> 0:04:51.760 that's already lit, and that's what lets us see it. 0:04:52.680 --> 0:04:55.000 And so he was just thinking it was an innate 0:04:55.200 --> 0:05:00.440 ability within the human eye and presumably animal eye as well. 0:05:01.000 --> 0:05:04.640 Epicurus had a totally different take on it. The philosopher 0:05:04.680 --> 0:05:07.920 known for emphasizing the pursuit of a happy life through 0:05:08.200 --> 0:05:12.800 eliminating fear and pain, which sounds nice, felt that objects 0:05:12.839 --> 0:05:18.160 themselves were emitting this light, that they were emitting this 0:05:18.400 --> 0:05:22.479 visible ray that our eyes could detect. So our eyes 0:05:22.520 --> 0:05:26.839 are detectors, but the objects themselves are emitting this, and 0:05:26.920 --> 0:05:29.840 that as a result, we could see light coming from 0:05:29.920 --> 0:05:32.760 the objects. Again, this doesn't really hold up when you're 0:05:32.760 --> 0:05:34.680 wandering around your house in the dark and you bark 0:05:34.720 --> 0:05:36.800 your ship on a coffee table. But what he was 0:05:36.880 --> 0:05:39.720 saying was that, all right, you're in a well lit area. 0:05:40.279 --> 0:05:44.360 Every single object that has this thing in it allows 0:05:44.400 --> 0:05:47.520 you to see it because it's emanating this energy that 0:05:47.560 --> 0:05:51.760 your eyes can detect. So a little closer to being 0:05:51.760 --> 0:05:55.840 correct than Pythagoras, but still missing stuff. Now you also 0:05:55.839 --> 0:05:58.200 had philosophers who started to get a little closer to 0:05:58.279 --> 0:06:01.920 what we know to be the truth that light can 0:06:01.960 --> 0:06:05.839 reflect off surfaces, bouncing off of them, or that it 0:06:05.880 --> 0:06:10.640 can pass through certain types of material like glass or water. 0:06:11.360 --> 0:06:14.640 But when it does, when light travels from that and 0:06:14.880 --> 0:06:18.160 hits something like the surface of glass or the surface 0:06:18.200 --> 0:06:23.080 of water, it bends, the light changes direction. Now these 0:06:23.120 --> 0:06:29.479 observations gradually lead to later smarty pants folks crafting lenses 0:06:29.880 --> 0:06:33.919 intended to bend light in specific ways. Not just you 0:06:33.960 --> 0:06:36.280 know it, not just it bends light, but I want 0:06:36.320 --> 0:06:39.240 to bend light so that it goes to this specific point. 0:06:39.920 --> 0:06:44.279 And an Arabic polymath in what is today known as 0:06:44.320 --> 0:06:49.839 Iraq even al hythem I figured that the human eye 0:06:49.880 --> 0:06:52.200 was doing the same sort of thing as a surface 0:06:52.240 --> 0:06:56.160 of glass or water. That light when it goes into 0:06:56.240 --> 0:07:01.440 the human eye would end up being directed. And also 0:07:01.839 --> 0:07:04.039 that light when it's going out in the world, it's 0:07:04.080 --> 0:07:07.360 bouncing off of objects, and it's the light bouncing off 0:07:07.400 --> 0:07:11.560 those objects that passes through the human eye against bent 0:07:11.640 --> 0:07:14.720 in a way where we can perceive it, and thus 0:07:14.760 --> 0:07:18.760 that's how vision works. This was around one thousand CE, 0:07:19.160 --> 0:07:24.840 or a d if you're using the more common nomenclature. Now. 0:07:24.960 --> 0:07:29.680 By the early seventeen hundreds we had Isaac Newton proposing 0:07:29.720 --> 0:07:34.760 that light was made of little corpuscles, little particles. In 0:07:34.760 --> 0:07:39.600 other words, that light really was made up of some tiny, tiny, 0:07:39.680 --> 0:07:44.040 tiny little piece of something. And it made some sense 0:07:44.720 --> 0:07:48.320 because light travels in a straight line, and it bounces 0:07:48.400 --> 0:07:51.200 off objects, just as a physical particle would do. Like 0:07:51.240 --> 0:07:53.560 if you had a tennis ball, then you threw it 0:07:53.560 --> 0:07:55.520 at a wall, it would bounce off the wall, and 0:07:55.960 --> 0:07:59.600 depending on the angle you threw the ball at and 0:07:59.640 --> 0:08:02.080 then that it hits the wall at, it's going to 0:08:02.200 --> 0:08:05.440 bounce in a specific way. Well, what Newton was saying, 0:08:05.640 --> 0:08:07.360 light appears to be doing the same thing. So it 0:08:07.440 --> 0:08:09.720 must be made of lots of tiny little tennis balls, 0:08:10.040 --> 0:08:12.320 although he didn't say tennis balls, but you know, just 0:08:12.400 --> 0:08:17.160 to continue the analogy. Others, however, would describe light as 0:08:17.200 --> 0:08:21.160 behaving like a wave, like a sound wave. And as 0:08:21.200 --> 0:08:24.640 it would turn out, both explanations were kind of right. 0:08:24.800 --> 0:08:28.640 Light behaves as a wave and a particle, but we 0:08:28.680 --> 0:08:31.520 wouldn't be sure about that for you know, a couple 0:08:31.640 --> 0:08:35.120 hundred years. But thinking about light as either a particle 0:08:35.240 --> 0:08:38.520 or a wave helps us understand what it's doing when 0:08:38.559 --> 0:08:42.680 it encounters other stuff. So let's start by thinking of 0:08:42.880 --> 0:08:46.320 as a ray of particles, and it's a ray that 0:08:46.360 --> 0:08:49.920 travels in a straight line until it encounters something else. 0:08:50.520 --> 0:08:52.680 And let's talk about how light interacts with stuff. So 0:08:52.760 --> 0:08:56.240 first up, as reflection, This is when light bounces off 0:08:56.280 --> 0:08:59.840 of a surface like a mirror or a tree where 0:08:59.840 --> 0:09:03.319 you our face. So light will bounce off a smooth 0:09:03.360 --> 0:09:05.800 surface at an angle equal to the angle of the 0:09:05.840 --> 0:09:10.000 incoming ray, making with the surface like there's a thing 0:09:10.080 --> 0:09:14.120 called the angle of incidents, and so you can predict 0:09:14.160 --> 0:09:16.600 what that angle is going to be if you're working 0:09:16.600 --> 0:09:19.839 with a perfectly smooth surface. This is what we call 0:09:19.880 --> 0:09:24.800 the law of reflection. However, we don't have perfectly smooth surfaces. 0:09:24.880 --> 0:09:28.000 If we did, then yes, you would see light bend 0:09:28.000 --> 0:09:29.920 in this way or reflect off in this way every 0:09:29.920 --> 0:09:34.120 single time. But we don't have perfectly smooth surfaces. Instead, 0:09:34.800 --> 0:09:39.480 we've got surfaces that have imperfections. And because of this, 0:09:39.559 --> 0:09:43.360 and because the wavelengths of light are very very very small, 0:09:44.080 --> 0:09:47.240 light will bounce off at all sorts of angles because 0:09:47.480 --> 0:09:51.040 again not perfectly smooth. This is why something like a 0:09:51.120 --> 0:09:54.240 tabletop won't disappear if you change your angle of view, 0:09:54.880 --> 0:09:57.080 right like if it if the light bounced in a 0:09:57.200 --> 0:10:00.600 very specific way because you had a perfectly smooth table, 0:10:01.480 --> 0:10:03.920 well that would mean that if you moved out of 0:10:04.000 --> 0:10:06.480 the angle of incidents, you would no longer see the 0:10:06.520 --> 0:10:09.360 tabletop because there will be no light bouncing off of 0:10:09.400 --> 0:10:12.080 it that you could see, which is kind of weird 0:10:12.120 --> 0:10:14.480 to think about, like the idea that something exists in 0:10:14.640 --> 0:10:19.440 one perspective, but at another it seems to not exist anymore. 0:10:19.440 --> 0:10:22.360 It does, you just can't see it. There are other 0:10:22.400 --> 0:10:24.920 reasons why it's gonna be don't have perfectly smooth tabletops. 0:10:24.920 --> 0:10:27.160 The big one being that if you had a perfectly 0:10:27.160 --> 0:10:29.440 smooth tabletop, there will be no friction. If you said 0:10:29.440 --> 0:10:31.760 anything on the surface of the tabletopic could slide all 0:10:31.760 --> 0:10:35.319 over the place. But we'll leave that beat. But then 0:10:35.360 --> 0:10:39.720 you've got absorption. Okay, so stuff can absorb light. Now, 0:10:39.720 --> 0:10:41.600 I'm sure you all know about the spectrum of light. 0:10:41.600 --> 0:10:43.960 We're gonna be talking about a lot in this episode. 0:10:44.440 --> 0:10:49.000 That's the old roy g biv red, orange, yellow, green, blue, indigo, 0:10:49.080 --> 0:10:51.440 and violet. That's the order that you would see if 0:10:51.440 --> 0:10:53.800 you were to see a rainbow. Well, that happens to 0:10:53.800 --> 0:10:56.120 be the spectrum of visible light. It's going from the 0:10:56.240 --> 0:11:00.800 longest wavelength red to the shortest violet. But we're gonna 0:11:00.840 --> 0:11:03.720 talk more about wavelengths in a little bit, and a 0:11:03.760 --> 0:11:08.600 lot of matter can absorb certain wavelengths of light. That 0:11:08.640 --> 0:11:11.800 means those wavelengths do not get reflected back at you 0:11:11.960 --> 0:11:16.040 when the light hits that object. For example, chromium, the 0:11:16.040 --> 0:11:19.600 stuff and rubies that makes them red, absorbs the green 0:11:19.679 --> 0:11:23.439 and blue wavelengths of light, so the only stuff that's 0:11:23.440 --> 0:11:26.360 getting reflected back is in the red wavelengths of light. 0:11:26.760 --> 0:11:30.079 So rubies appear red to us because the other wavelengths 0:11:30.080 --> 0:11:33.320 of light have been absorbed by the gem. If you 0:11:33.360 --> 0:11:36.840 had something that could absorb all wavelengths of light, it 0:11:36.920 --> 0:11:41.120 would look black, like pure black, as if there were 0:11:41.160 --> 0:11:45.160 avoid rather than you know, whatever the thing is. And 0:11:45.200 --> 0:11:48.360 there are special paints out there that absorbed nearly all 0:11:48.520 --> 0:11:51.600 visible light hitting them, and seeing stuff covered in that 0:11:51.640 --> 0:11:55.280 paint is trippy because it looks like there's just a 0:11:55.280 --> 0:12:00.680 a thing shaped void in a physical space. So one 0:12:00.679 --> 0:12:04.720 example I've seen as an apple that's been half painted 0:12:05.520 --> 0:12:10.480 uh with this special super uber black paint, and you 0:12:10.559 --> 0:12:14.520 put the apple on a little rotating pedestal, and what 0:12:14.640 --> 0:12:17.320 you'll see is that when the apple rotates so that 0:12:17.440 --> 0:12:19.880 the red of the apple starts to give way to 0:12:20.040 --> 0:12:24.360 the void black, it looks like half the apple is missing, 0:12:24.880 --> 0:12:28.280 but you're not seeing the inside of the apple. It's 0:12:28.320 --> 0:12:30.640 just the half the apple is just a black shape, 0:12:30.960 --> 0:12:33.080 and if it turns all the way around, it's like 0:12:33.080 --> 0:12:35.720 the apple doesn't exist anymore. You just see a black 0:12:36.840 --> 0:12:41.520 field in the shape of an apple. It's crazy. You 0:12:41.520 --> 0:12:43.080 could do that with a pumpkin and you would have 0:12:43.080 --> 0:12:45.920 a pumpkin shaped hole instead of a jack ol Internet Halloween, 0:12:45.960 --> 0:12:48.360 which would be super awesome in the daytime, wouldn't be 0:12:48.400 --> 0:12:51.760 so effective at night. But it is really neat stuff. 0:12:51.880 --> 0:12:54.720 By the way, there are different types of this ultra 0:12:54.800 --> 0:12:59.640 black paint out there. There's one kind that was heavily trademarked, 0:12:59.640 --> 0:13:02.280 and then someone else went and developed a similar kind, 0:13:02.800 --> 0:13:05.920 specifically because they felt it was wrong for someone to 0:13:05.960 --> 0:13:09.880 try and trademark a color. But yeah, that's that's a 0:13:09.920 --> 0:13:13.600 topic for another episode. Then we have when light goes 0:13:13.640 --> 0:13:18.640 from one transparent medium to another, when it passes through 0:13:18.679 --> 0:13:23.200 a barrier, and then what happens to it. So this 0:13:23.240 --> 0:13:26.320 would be like when light travels through air, hits the 0:13:26.320 --> 0:13:29.880 surface of water or air, and it hits a lens. 0:13:30.600 --> 0:13:34.880 That's when you get refraction. Now I'll explain what refraction 0:13:34.960 --> 0:13:38.520 is because it's very important for our discussion. But first 0:13:38.600 --> 0:13:51.000 let's take a quick break. Okay, Before the break, I 0:13:51.040 --> 0:13:55.959 was talking about refraction. Refraction is when light does pass 0:13:56.040 --> 0:13:59.480 from one medium to another and it changes speed. Now 0:13:59.520 --> 0:14:03.800 that might sound weird because everyone knows light is the 0:14:03.840 --> 0:14:07.240 fastest stuff in the universe. It is the speed limit 0:14:07.440 --> 0:14:10.600 of the universe. There is nothing faster than light. In fact, 0:14:10.800 --> 0:14:13.960 we use the speed of light as a constant. The 0:14:14.120 --> 0:14:19.760 famous equation E equals mc squared is referencing the speed 0:14:19.760 --> 0:14:23.800 of light. That's energy equals the mass of something times 0:14:24.360 --> 0:14:27.040 the square of the speed of light. So if it 0:14:27.200 --> 0:14:30.359 is a constant, how can the speed of light change? 0:14:31.400 --> 0:14:34.400 Those two things don't make sense. Well, when we talk 0:14:34.440 --> 0:14:38.000 about the speed of light as a constant, we're referring 0:14:38.240 --> 0:14:44.000 to light traveling through a vacuum, an empty medium, outer space, 0:14:44.880 --> 0:14:48.240 outer space where you've got a true vacuum. But when 0:14:48.320 --> 0:14:53.240 light hits a medium like say an atmosphere or water, 0:14:53.800 --> 0:14:57.400 or the lens of a telescope or glasses, it does 0:14:57.440 --> 0:15:00.240 slow down a little. It changes speed. It can't get 0:15:00.320 --> 0:15:03.480 faster than it can through the vacuum of space. That's 0:15:03.480 --> 0:15:06.880 the as fast as anything can go. But if it 0:15:07.000 --> 0:15:12.000 hits something like trans transparent medium, it will change speed. 0:15:12.600 --> 0:15:15.960 It slows down. Think of it kind of like walking 0:15:16.240 --> 0:15:19.160 in just the open air, like you're going out for 0:15:19.200 --> 0:15:23.600 a stroll, versus trying to walk in a swimming pool. 0:15:24.200 --> 0:15:25.840 You know, when you're in a swing pool and you're 0:15:25.840 --> 0:15:29.000 trying to walk across the pool, you feel the resistance 0:15:29.000 --> 0:15:31.880 of all that water that slows you down, Whereas when 0:15:31.880 --> 0:15:35.720 you're walking through just you know, the room, then all 0:15:35.760 --> 0:15:37.840 you're doing is walking through air. You have much less 0:15:37.880 --> 0:15:40.200 resistance and you're able to go much more quickly. It's 0:15:40.360 --> 0:15:44.440 very similar to that. So when light changes speed as 0:15:44.480 --> 0:15:48.800 it passes into a new medium, it bends. The amount 0:15:48.840 --> 0:15:52.160 of bending or angle of refraction depends upon how much 0:15:52.200 --> 0:15:55.960 slower the light will travel as it moves through the 0:15:56.000 --> 0:15:59.440 new medium. In fact, we call this the refraction index 0:15:59.520 --> 0:16:02.800 when we look at the different transparent media and we 0:16:02.880 --> 0:16:05.800 say all right, well, based upon this difference, will know 0:16:05.920 --> 0:16:08.400 how much of a bend will see in the light. 0:16:08.880 --> 0:16:10.600 So if you've ever seen like a shaft of light 0:16:11.160 --> 0:16:16.160 shining down to a a surface of water, then you're 0:16:16.400 --> 0:16:18.680 looking at like a cross section, like you can see 0:16:18.680 --> 0:16:22.360 both above and below the water. You actually see where 0:16:22.600 --> 0:16:24.760 the bend is there. Or if you want to do 0:16:24.800 --> 0:16:26.960 a really easy one, you get a glass you fill 0:16:27.000 --> 0:16:30.080 it up with water, like maybe to the halfway point. 0:16:30.480 --> 0:16:32.640 Put a straw on that glass, and then you look 0:16:32.680 --> 0:16:34.680 at the glass from the side, and you'll see that 0:16:34.800 --> 0:16:38.000 the straw appears to bend at the point where it 0:16:38.520 --> 0:16:43.320 crosses over into the water. That's because of this refraction 0:16:43.560 --> 0:16:46.400 and this refractive index and the difference between the two, 0:16:46.600 --> 0:16:50.120 and we get that that little bend there. So a 0:16:50.240 --> 0:16:53.400 lens is shaped in such a way as to bend 0:16:53.480 --> 0:16:55.800 light to a specific focal point. If we're thinking of 0:16:55.840 --> 0:16:58.680 it in the terms of rays, right, array coming in 0:16:59.160 --> 0:17:02.360 at the edge of the lens, where it is more narrow, 0:17:02.760 --> 0:17:05.880 is going to be bent a certain way. Array coming 0:17:05.920 --> 0:17:08.359 in through the center of the lens is going to 0:17:08.440 --> 0:17:10.720 go in a certain direction. And then at the very 0:17:10.720 --> 0:17:13.639 bottom of the lens, which is again perhaps more narrow 0:17:13.720 --> 0:17:18.160 we're looking at our typical lens, would then be bent 0:17:18.359 --> 0:17:20.680 in a certain way so that these these different bent 0:17:20.960 --> 0:17:24.760 rays of light will converge at a point where we 0:17:24.800 --> 0:17:27.359 can get, say, an image. This is how we create 0:17:27.440 --> 0:17:31.560 things like corrective lenses for glasses, and bending light is 0:17:31.600 --> 0:17:38.159 really the secret sauce. In most invisibility technologies or cloaking technologies. 0:17:38.760 --> 0:17:41.280 This is pretty easy to understand. There's another way to 0:17:41.320 --> 0:17:43.280 look at this, by the way, and in fact, I 0:17:43.320 --> 0:17:45.440 would argue the other way to look at it makes 0:17:45.480 --> 0:17:48.600 it even easier to understand, which is to think of 0:17:48.640 --> 0:17:53.080 the incoming light as waves and think of the lens 0:17:53.080 --> 0:17:56.160 like let's say that we've got our our regular convex 0:17:56.280 --> 0:17:59.920 lens where it's narrower at the top and bottom and 0:18:00.080 --> 0:18:03.840 thickest in the middle. Right, the wave hitting the top 0:18:03.920 --> 0:18:07.000 and the bottom, those waves are going to be slowed 0:18:07.040 --> 0:18:12.120 down less than the wave that's hinting hitting the center 0:18:12.160 --> 0:18:16.640 of that lens, because the the material is thinner at 0:18:16.640 --> 0:18:19.800 the top and bottom and thicker in the middle. So 0:18:20.080 --> 0:18:22.200 the waves at the top and bottom slow down a 0:18:22.240 --> 0:18:24.399 little bit, but not a lot. The wave in the 0:18:24.400 --> 0:18:26.720 middle slows down the most. And what you get on 0:18:26.760 --> 0:18:30.280 the other side of the lens is this converging wave, 0:18:30.960 --> 0:18:34.480 being the wave is starting to get uh smaller and 0:18:34.520 --> 0:18:39.000 smaller to a focused point because of the the speed 0:18:39.560 --> 0:18:43.080 at which it has traveled through that lens, and it converges, 0:18:43.359 --> 0:18:47.040 and that's where you get your your focal point. That's 0:18:47.040 --> 0:18:49.360 another way to think about it. It becomes really important 0:18:49.359 --> 0:18:54.320 when we start talking about invisibility technologies. All right, something 0:18:54.400 --> 0:18:56.159 else we have to know about light. It's part of 0:18:56.160 --> 0:18:59.320 the electro magnetic spectrum. As I'm sure you're all know, 0:18:59.600 --> 0:19:03.400 the visible of lights just one tiny part of of 0:19:03.440 --> 0:19:05.720 a band of frequencies that make up what we call 0:19:05.880 --> 0:19:10.040 light like light that we can see. That's one tiny 0:19:10.080 --> 0:19:14.080 slice of light. Overall. There's also infrared light, which is 0:19:14.119 --> 0:19:17.280 on one side of the visible spectrum, an ultraviolet light, 0:19:17.640 --> 0:19:21.040 which is on the opposite side. We cannot see infrared 0:19:21.080 --> 0:19:24.560 and ultra violet directly. We can create technologies that let 0:19:24.760 --> 0:19:29.439 us detect this kind of light and then see it 0:19:29.600 --> 0:19:32.600 in the sense of converting that into light that we 0:19:32.640 --> 0:19:37.960 can actually directly perceive. Right, So, if you have infrared goggles, 0:19:38.800 --> 0:19:41.520 you're not actually looking at infrared light. What you're looking 0:19:41.520 --> 0:19:46.840 at is a interpretation of infrared that's been fed into 0:19:47.520 --> 0:19:50.440 technology that gives you light that you can actually see, 0:19:50.720 --> 0:19:54.000 so that things that are really hot appear red, and 0:19:54.040 --> 0:19:56.919 things that are cooler might appear blue, that sort of stuff. 0:19:57.320 --> 0:20:00.160 But the red and blue, that's red and blue. That's 0:20:00.200 --> 0:20:03.840 not infrared. It's just it's been interpreted through the technology. However, 0:20:04.040 --> 0:20:06.320 you took the the goggles off entirely, you wouldn't be 0:20:06.359 --> 0:20:08.240 able to see anything because everything would be dark. That 0:20:08.320 --> 0:20:10.320 kind of thing. It's night vision goggles work on a 0:20:10.359 --> 0:20:18.160 similar idea. So that's where light fits. But then beyond light, 0:20:18.600 --> 0:20:21.640 you've got all sorts of different types of electro magnetism, 0:20:22.320 --> 0:20:24.639 Like you have different flavors of it if you would, 0:20:24.680 --> 0:20:28.760 like you've got radio waves that's on the the longest 0:20:29.160 --> 0:20:33.119 wavelength side of the electromagnetic spectrum, and then on the 0:20:33.200 --> 0:20:37.080 opposite side, on the shortest wavelength side, you have gamma radiation. 0:20:37.800 --> 0:20:42.280 So what determines the nature of this electromagnetism, what determines 0:20:42.320 --> 0:20:44.360 what it can do and what we can use it for, 0:20:45.359 --> 0:20:48.800 is its wavelength or its frequency. The two are related. 0:20:49.320 --> 0:20:53.080 The longer the wavelength, the lower the frequency. The shorter 0:20:53.160 --> 0:20:55.720 the wavelength, the higher the frequency. But here's the thing. 0:20:56.400 --> 0:21:00.440 All of these frequencies are traveling at the same eat. 0:21:00.440 --> 0:21:03.880 That electromagnetic speed is the speed of light, so they're 0:21:03.920 --> 0:21:07.040 all traveling at the same speed. It's just that they 0:21:07.080 --> 0:21:11.040 have different lengths of of waves, right. So radio waves 0:21:11.040 --> 0:21:15.159 are very very very long, gamma waves are very very 0:21:15.280 --> 0:21:18.040 very short. They both travel at the speed of light. 0:21:18.400 --> 0:21:20.800 But it means that the number of waves that pass 0:21:20.880 --> 0:21:24.119 you in a given second are very different for radio 0:21:24.160 --> 0:21:28.560 than it is for gamma, because more of the gamma 0:21:28.640 --> 0:21:32.240 can pass you in the second than the radio waves 0:21:32.280 --> 0:21:35.080 because the length is so much shorter. Well, since visible 0:21:35.160 --> 0:21:39.200 light occupies a range of frequencies, we can encounter some 0:21:39.320 --> 0:21:43.120 challenges when we start to think about ways to manipulate light. 0:21:43.920 --> 0:21:49.280 So there's this effect called chromatic aberration. Sometimes it's called 0:21:49.359 --> 0:21:53.320 chromatic distortion, which be a great name for a band. 0:21:54.320 --> 0:21:59.359 Maybe you just cover social distortion songs. Anyway, Chromatic distortion 0:21:59.400 --> 0:22:02.640 occurs because visible light is made up of a band 0:22:03.160 --> 0:22:06.159 of wave wavelengths of light. You know, red has the 0:22:06.240 --> 0:22:12.320 longest wavelengths invisible light, Violet has the shortest wavelengths, and 0:22:12.359 --> 0:22:16.480 when light hits a refractive surface like a lens, not 0:22:16.840 --> 0:22:20.240 all these wavelengths are going to bend at quite the 0:22:20.359 --> 0:22:24.240 same angle. So you might notice that some parts of 0:22:24.240 --> 0:22:28.160 an image have little borders or fringes of color around them. 0:22:28.160 --> 0:22:32.040 And that's because that wavelength of light, let's say it's red, 0:22:32.600 --> 0:22:35.800 bent at a slightly different angle from the other wavelengths, 0:22:35.920 --> 0:22:39.480 and so you get this kind of halo effect. Now, 0:22:39.480 --> 0:22:41.600 the reason I bring this up is that one of 0:22:41.640 --> 0:22:45.040 the biggest challenges when it comes to creating invisibility technology 0:22:45.640 --> 0:22:49.400 is that the methods we might use could work differently 0:22:49.720 --> 0:22:53.359 with some parts of the visible light spectrum from others, 0:22:53.960 --> 0:22:56.240 and you might end up with the technology that can 0:22:56.280 --> 0:23:01.600 redirect certain parts of the visible spectrum in a specific way, 0:23:01.640 --> 0:23:05.320 but not all of the visible spectrum. And that would 0:23:05.359 --> 0:23:07.600 mean that you would still be able to see the 0:23:07.640 --> 0:23:10.639 cloak or the cloaked object, but it would look kind 0:23:10.640 --> 0:23:12.720 of funny because you wouldn't see all the colors you 0:23:12.800 --> 0:23:15.200 normally would, or it would appear to be a different 0:23:15.200 --> 0:23:19.600 color than what it quote unquote really is. If you 0:23:19.640 --> 0:23:22.000 want to think about another way, imagine that you've got 0:23:22.000 --> 0:23:25.120 a gap that's just wide enough to let visible light 0:23:25.200 --> 0:23:29.560 from green to violet go through. So anything that's green 0:23:29.640 --> 0:23:32.280 to violet and the visible spectrum can pass through this 0:23:32.400 --> 0:23:36.119 tiny little gap. But that would mean that wavelengths that 0:23:36.200 --> 0:23:38.960 were in red, orange, and yellow light because of roy 0:23:39.040 --> 0:23:43.560 g BIV, those wavelengths would bounce off because the gap 0:23:43.680 --> 0:23:47.840 is too small for these wavelengths to pass through it. 0:23:47.840 --> 0:23:50.400 It's it's too narrow. That's kind of what I'm going 0:23:50.480 --> 0:23:54.239 with here, all right, So when we come back, we're 0:23:54.280 --> 0:23:56.560 going to talk about some of the technology is meant 0:23:56.560 --> 0:24:01.080 to make something invisible, and we're gonna start with stealth 0:24:01.400 --> 0:24:15.320 technology after we take this quick break. All right. I'm 0:24:15.359 --> 0:24:18.159 I'm a kid of the seventies and eights, and I 0:24:18.240 --> 0:24:23.240 remember when the stealth bomber was becoming big news. It 0:24:23.320 --> 0:24:27.080 was such a cool science fiction technology. We had heard 0:24:27.080 --> 0:24:30.639