Stuff You Should Know - How Mirrors Work

Episode Date: September 14, 2010

Whether using polished metal surfaces or clear glass, human beings have enjoyed admiring their reflections for centuries. In this episode, Josh and Chuck reflect on the types, mind-melting physics, superstitions and rather interesting history of mirrors. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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like what we would call a jack move or being robbed. They call civil acid work. Be sure to listen to the War on Drugs on the iHeart radio app, Apple Podcast, or wherever you get your podcasts. Brought to you by the reinvented 2012 Camry. It's ready, are you? Welcome to Stuff You Should Know from HowStuffWorks.com. Hey, and welcome to the podcast. I'm Josh Clark. There's Charles W. Chuck Bryant. We're about to talk about mirrors. Nice setup. It's a sink, huh? How are you? Were you in the mirrors growing up? Look, now that we said, you know, I did it succinctly, we're going to just

blow like three minutes. Yeah, right. No, I was asking you if you were in the mirrors growing up. In the mirrors growing up? Yeah, I mean, that doesn't every kid go through a phase where they're like very obsessed with their looks and mirrors and things. Oh yeah, I was into myself. I wasn't into mirrors. They were just a means to an end, you know? Yeah, but I was reading this and I kind of was just thinking to myself, remembering, laughing about, I remember being like 15 and like stopping to look at mirrors any time there was one to see what I look like. Yeah. And now I just, I break them. I'd forgotten all about that phase of my life though until you just brought it up. Yeah, remember that? Yeah, it's nice to be able to not look at a

mirror. Like some days I'll go out, you know, after getting ready in the morning and I have no idea what I actually look like. But I'm so, and this is this cross-pollination with an earlier podcast, I suffer from body dysmorphic disorder so badly that I don't really know what I look like anyway. What do you think you look like? I think I look a bit like the guy from taxidermia. Yeah. What's that? It's not plus. Okay. Well, you don't, my friend. I don't even know what he looks like, but I can tell you don't look like him. I appreciate that, Chuck. Chuck, do you want to hear what I had in store? Like I could not come up with an intro for this. Let's hear it. Webster's defines mirrors. I'm kidding. I was

going to say something equally bad though. It was going to be something along the lines with mirrors are ubiquitous. I've seen at least six of them today. Wow. They weren't always that way though, Chuck. Well, it says in the article here that full-length mirrors have only been around 400 years. That didn't seem right. That's not right. Oh, really? No. Full-length mirrors, there's a type of full-length mirror that has been around for about 400 years. Full-length mirrors, as far as I know, are mirrors capable of reflecting a full image of a person, have been around since about the first century AD, actually. Wow. And mirrors, us using surfaces, polished surfaces, to see our own reflection, has been around since about 6000 BC. Holy cow. Yeah. The earliest ones

were found in Anatolia, Turkey. Wow. And they're polished obsidian. Yeah. This is a volcanic glass. Yeah. So it's dark. That's interesting, but it still produced the best reflection, I guess, at the time. At the time, sure. Yeah. I mean, you got to go with what we have to work with, right? Well, yeah. But then after that, it led them to silver and bronze and copper polished reflections, basically. And Chuck, I don't know if you've ever held a hunk of copper or bronze. I haven't. Or silver? I have. Okay. It's heavy. Yeah, it's real heavy. Right? So this actually limited the size of mirrors for centuries, right? Yeah, and they were just kind of decorative at first, too, right? I think so. And you also had to be extremely rich to own one of these. Sure. Right. And then

around, I think, the Middle Ages, we became capable of making glass. Right. And all of a sudden, it was like mirror technology just takes a huge leap forward. Well, true, but not super forward because the sand was pretty impure back then. They used to make the glass. So I think they said in the article, it wasn't until like the Renaissance that it kind of really started becoming a little more polished, if you will. Terrible. And then the Venetians are who really, with a glass and everything, they just took and ran with it. Well, even still, if you successfully made a mirror, it was probably extremely expensive as well because they were so rare. The process of manufacturing a mirror very infrequently produced a usable mirror.

So what you're doing was adhering melted molten metal onto glass, which almost always broke the glass. Sure. So when it didn't, I'm sure you're just like, oh my God, it's the first one in seven years. I'm so excited. Right. But then when I was reading this article, I didn't really think about it. That's what a mirror is, isn't it? I've even seen the back of mirrors and been like others, like metal looks like spray painted on the back. That's exactly right. And that was a process, what's it called, silvering that was invented by a guy named Justice Von Liebig. And in 1835, he figured out how to spray a very thin layer of silver or aluminum on one side of a glass. And they're my friend, you have the modern mirror. Yeah. And now they I think they make it now by

heating aluminum in a vacuum and kind of much the same way or different methods, but the same same concept. Right. Go ahead. Well, I wanted to say when you were talking about the Renaissance, the Venetians, right, were they, I guess they had the secret of mirrors under wraps like the Masons? Very much so. And if you were a mirror maker and it got out that you had told someone how to make mirrors, you were frequently killed, right? Yeah. Yeah. Trade secret. But when mirrors were introduced, when good mirrors were introduced, not polished obsidian, things changed a little bit, especially with art, right? Yeah, I never really considered that, but it spawned something that would become a hallmark of the art world, which is the self portrait. Right. Before that, you

couldn't draw yourself because you could not see yourself. That's exactly right. And you could, but I mean, you're going to use like maybe a pond or well, yeah, sure. Piece of polished metal or something like that. Imagine like going out and looking at a pond and going back and sitting down now as opposed to having a mirror there. Yes. Really simplified it. It's also not coincidental that good mirrors came about at the same time that linear perspective was introduced into art. What? Yeah, there's a guy named Filippo Brunelleschi. Filippo Brunelleschi? Nice, Chuck. Thank you for doing that. And he, he, I guess, discovered linear perspective because I think it's one of the things that was always there. Right. We just stumbled upon it through mirrors. Oh, really? That's how

we figured it out. Yeah, because if you look at a mirror, all of a sudden linear perspective really comes into focus, if you will. Well, and then scientists said, hey, we could use these to make like reflecting telescopes. And that was what you was at. That was a long time ago. The first reflecting telescope was invented by a guy named James Bradley in 1721, just off the top of my head. Very well done. And the mirrors were also used by a very, very famous scientist, early scientist named Archimedes, supposedly. Yeah. I wrote an article on Archimedes death ray. Oh, did you write that? Yeah. Did you ever read it? I did back in a while ago, just out of interest. How about that? Thanks a lot, man. Sure. Did you see in it some, I can't remember. It was one of the Ivy League

schools. They tried to set things on fire with this system of mirrors that Archimedes specifically used. Well, MIT did. That's who it was. And they succeeded. Yes. And the mythbusters claimed it was busted. Like they set a small fire, but I think they busted it because they said it wasn't enough to like sink a ship. Yeah. But MIT, I mean, they, they caused quite a fire on that boat. Sure. And of course they had, I mean, I saw the setup online today. It was pretty massive. Yeah. I don't know if Archimedes had that kind of technology, or at least that many mirrors in this disposal, or maybe he did. And plus they had, I think they used pretty good mirrors too. Yeah. Well, it was legend though. They don't know if the Archimedes thing is true, right?

Right. We know that he invented the water screw, and that saved countless lives. What's that? It's a way to deliver water from the ground top side. Oh, really? Yeah. Cool. You'll have to check it out. Smart dude. So Chuck, we now know the comprehensive, broad strokes of the history of mirrors, right? Yes. Let's talk about mirror physics. We work for HastuffWorks.com, which means we're pretty much obligated to discuss the physics of whatever we're talking about any time it applies, right? That's true. And mirrors are definitely one of those times. Yes. So Chuck, take it away. Well, I can cover the first part because it makes sense to me. The law of reflection, Josh says that when you bounce array of light off a surface,

it bounces back off in a certain way. And it is, the angle of incidence is when it comes in, the angle of reflection, when it bounces off, and it matches. So the way they pointed out in the article, which makes sense to me, is like at sunset, the sun's very low on the horizon, so it bounces off at a low angle or approaches the water at a low angle, like at a lake, let's say. Right. Then it bounces off of that lake at that same low angle, like right into your face. Right. But it seems brighter. If the sun's overhead though, the sunlight is coming down under the lake and it's reflecting back up basically over your head. Yeah. You're looking at a horizontal angle pretty much. Right. And this is happening on a vertical angle.

Yeah. That's why you'll get like more glare at a sunrise or a sunset scenario. Right. And what you're saying, the angle of incidence equals the angle of reflection, right? Indeed. If you take, if a beam of light is shot at a 90 degree angle, or no, let's say a 80 degree angle, it's going to bounce off at an opposite 80 degree angle. Right. So both are at 80 degrees, but if you look at the whole thing, the incidence and the reflection, it's going to cover 160 degrees. Right. Yes. Right. All right. So that's the first part. That's, that's how, that explains how light reacts with, with reflection. And that's where the smooth surface with, with most things,

like say, look at my hand, man. Take a look at these hands. Yes. The light that's bouncing off of them, what's giving us the ability to see these huge, awesome hands. They're not huge, are they? No. Are they smaller than average size? No, they're bigger than mine. I got small hands. I wouldn't say you have small hands. Let's see. No, those are like, those are totally normal. I don't have hair on the back of my hands either. I've got hair on my first knuckles. Yeah. Robin Williams. What's allowing us to see our hands right now and judge their size and scale is what's called diffuse reflection, which the light that's coming off of all of these

light bulbs right now are hitting all of these different areas, these different surfaces on my hands and bouncing off, it's being scattered. Right. The mirror, the highly reflective surface, what we have is called specular reflection. Right. And that is where it's pretty close to the law of reflection where the angle's coming in at one or the light's coming in at one angle and coming off the, at the same degree. Right. In the opposite direction. Right. Which is why we're allowed to see ourselves in a piece of glass with metal on the back. Yeah. And what this creates when you're looking at yourself is called the virtual image, right? I find this fascinating. Yeah, me too. And it's a little brain melty for me.

Of course. But at the same time, you realize like, well, you've grown up around mirrors the whole time and no one has any real concept of, of how they work. Right. Yeah. We just take for granted that they do work, but you don't really give much thought to how they're working. Right. Yeah. Like the Venus effect. Did you read about that? Yeah. That's explained that because this is where when we talk about, oh, actually the Venus effect is two different things and both of them kind of melt my brain that the left and right being reversed, which is not actually true. Right. And then the Venus effect. So let's talk about both of those. Okay. Well, the Venus effect basically just shows how little we can grasp or how little we grasp mirrors and how they work.

If you look at paintings of the Venus de Milo or Venus, the goddess, almost always she's holding a hand mirror. Yeah. And in the painting, you can see her face in the mirror, but she's looking at herself in the mirror. Right. And her face is painted in the mirror for the benefit of the viewer, but you take for granted that she's viewing herself when in actuality, if you could see Venus's face in the mirror, she wouldn't be able to see herself. She'd see you in the mirror. Right. Because of that angle or the law of reflection. Yeah. And that's the only way I finally understood that was when I remembered like in my film set days, when you shoot a person looking in a mirror, they don't see themselves in the mirror clearly because you would see the

camera behind them. Exactly. So the mirror is angled and it looks like they're looking at themselves and primping, but they're not seeing themselves. It's pretty cool. Right. So that makes sense to me now. It does, doesn't it? Yeah. Yeah. Okay. The other thing you were saying is left and right. Yeah. It's not actually left and right. Yeah. This one was a little brain melty, but I think I finally got it too. Okay. So consider that what you're not, what you're seeing isn't actually your reflection, but another version of yourself in the mirror world. Right. Right. If you look at it that way, then the mirror represents the halfway point. It's always halfway between you and your virtual self. Right. Right. Because your virtual self, that image of yourself

in the mirror is always twice as, it's always two times away from you with the mirror representing the halfway point. Right. So your two feet from the mirror and your virtual self is another two feet away from you. Right. You see what I'm saying? Yeah. And the left and right thing isn't really left and right. It's really front and back. That's right. That are reversed. You again think of yourself as the virtual image. Yes. You walk into the mirror world. You take, you go another two feet away from where you're just standing. So you're now, you're four feet away from where you're just standing and turn around. Right. Which is weird because it actually gives the virtual image something of its own identity, doesn't it? It does. It's a little creepy. Yeah. So when you're looking at a mirror,

it's not a reflection of you from the mirror's perspective. It's like that the one example they gave was if you wrote something on a piece of paper and then held that paper up to the light and looked at it from the back, it would appear backwards. Right. But it's not. Right. You're just behind it. Yes. Crazy, man. Isn't it? Yeah. It's pretty interesting stuff. And I got to say when you, two things, when you mentioned doing mirrors, I said to myself, huh, really? And then when we told Jerry what we were doing this on, she was like, huh, really? Yeah. But it's, I think it's much more interesting than I originally thought. Well, again, it's like the butterfly swings, you know, like we just have to know that if we're going to understand absolutely everything

that's going on in the world. Which is our mission. Yes. Should we talk about curved mirrors now? Yeah, because we were talking about virtual images. Yeah. There's actually a way to project a real image where this thing isn't in the mirror. It's outside of the mirror, but it's not really there. It's a projected image. Right. And that uses concave mirrors. You might be familiar with holograms. Yes. Right. Is that the same concept there? Yeah. It uses concave mirrors. And actually, if you want to see a really cool example of a hologram produced by a set of concave and flat mirrors, you should type in Mirage in YouTube and look for the one that's lowercase, just Mirage, and it's a little piggy. And it's pretty cool, the demonstration that this guy does. Oh, really?

Yeah. I'll check that out. But Chuck, there's concave and convex, right? Yeah. Convex is the one that curves outward and it reflects at a wider angle near the edges in the center. So things are actually smaller and you can cover more areas. So that's why they'll use those. They'll stick them on like your passenger mirrors so you can see more area around your car. Right. And it also notes, you know, objects are smaller than they appear, or closer than they appear. Right. Objects are smaller than they appear. But they are smaller than they appear, but that's not really, that doesn't matter. It's whether they're like in your backseat or not. Yeah. And they actually, there have been rumors over the years that department stores put convex mirrors, slightly

convex mirrors in their changing rooms to make you like appear taller and thinner in the clothing that you try on. Remember that Seinfeld where Elaine like buys that dress and she figured out that they had a skinny mirror and I think Barney's or Bloomingdale's. Yeah, I forgot about that. Yeah. I don't know. I think that's probably Urban Legend, but who knows? Chuck, the other one, like we said, was concave converging. We used those for holograms. They also used that to light the Olympic torch. Yeah, I didn't realize that either. I think that's a nod to Archimedes too. Probably so. You're probably a little more acquainted with convex mirrors. No, concave mirrors for like shaving or, you know, those horrible

mirrors that show your hair in detail. Those are awful. They really are. Don't ever look in those. Non-reversing mirror, which really is pretty simple. It's just two mirrors perpendicular to each other, right? Yeah, and the deal is with that, they meet at the angle and so you technically can see a non-reverse image, but you've got that line running down the center of you. Right. They don't make like a flat single non-reversing mirror. No, they don't. I think it's physically impossible. Yeah, it's not like they don't make it like they're not interested. It just can't be done. But what's funny is there's a guy named John Derby who has a patent in 1887 when he was alive. He had a patent for a non-reversing mirror by sticking

two mirrors together. I could get a patent for that. I could fill out the patent application for that. You could? Yeah, it's like take mirror A and stick it perpendicular to mirror B. Right. There, give me my patent. Well, but then John Derby's family would come after you. Hopefully it ran out by now just for simple-ness. Josh Two-Way mirrors. I've seen an every cop shakedown movie ever made. Yes. Now this is fascinating, Chuck. How does a two-way mirror work? Well, it's really pretty easy. It's just, it's the same concept of a mirror, but it's a very thin, it's very much a lighter reflection, the material they use. And the coated side, when it faces the lit room, some of the light reflects and some goes into the dark room behind it.

So basically, like you know, you can't, you can only see one way. Right. Because of the light, mainly. Right. So it's just like very thin reflective surface where if you're not lit, if you turn in, if you turn on lights in both rooms, you'd be able to see through that reflective surface, right? Yeah, it's all about the lighting. Yeah. And that's a movie. There, there's several movie mirror things that are done in like every movie. And that's one of them with the cop movie. And inevitably the person getting questioned will always walk right up and like be staring into the face of the person on the other side that they can't see. Right. And then the other favorite of mine, which one of the SNL shorts eight was the classic horror movie scene where you, where you

look in the medicine cabinet in the mirror and then you open the medicine cabinet and then you close it and the dude is right behind you. Yeah. That's a classic. It is. There's again on YouTube, I think there's a montage, like a four minute, 20 minute montage of that being used over and over and over. Hundreds of times, dude. And it still gets people. Yeah. But now that the whole spin is to do that and then there's not someone there. Right. And then they'll turn around and that's where they are or something. Yeah. Just jerking the audience around. That's in there too. Oh, it is? Yeah. Yeah. It's not just people closing. There's someone saying there's ones where they're not standing there. Yeah. I love those movie conventions that are, the other one too is

it doesn't have anything to do with mirrors, but the scene where you're, where someone is searching for the files and then the person's office after dark and you know, they're coming up the steps and they open the door and you're like, they're pinched and then they open the door and the person's gone and there's like a window open. Right. And it's just like the curtains. Yeah. Hundreds and hundreds of time is still done yet. I'm still like, oh my gosh, here they come. What about Poltergeist, that great classic mirror scene where the guy's like picking at that little blister and ends up pulling his whole face off? Yeah. That's pretty creepy. Yeah. Classic. Thank you, Toby Hooper. Did he make that? Yeah. Oh, God, that's right. Yeah, he directed it, right?

That's right. I always think he directed that. What else, Chuck? Well, there's some superstitions around mirrors and folklore. Summoning Bloody Mary by saying her names three times in a mirror or Candy Man, if you're a little more recent, breaking a mirror, supposedly bad luck because for seven years because they believe that the soul regenerates every seven years. Yeah. That explains it, doesn't it? Yeah. And that's why vampires have no soul. That's why they can't see themselves in mirrors. And a couple of them I haven't heard of are, if you give birth and look in a mirror too soon afterward, you will see ghostly faces peek out from behind the reflection. Right. I'd never heard that one, have you? No. I had heard of

sitting Shiva though. Yeah, what's the deal with that one? Well, if you're Jewish and somebody dies part of the mourning process is to cover all the mirrors in the house. Did you say that in the Talmud? Shut up, Chuck. Also, we have gotten conflicting information about whether or not it is taboo among Judaism to be cremated. Did you notice? Yeah. And I'll stand behind what we found, which was that reform Jews will do it, but it's still not encouraged, but it is actually forbidden in the actual Jewish text. Right. So there. Fine. Is that it? I think that's about it. Oh, New Year's Eve, right? Yeah, I hadn't heard of this one either. If you go up to a mirror on New Year's Eve with a candle in your hand and you say the name of a dead person, probably a dead

loved one, in a loud voice, their face should appear in the mirror. Never heard that. And this is my favorite one, the ancient Chinese mythology. You know how you see weird movement in like the corner of a mirror every once in a while? Have you ever noticed that? Sure. I just figured it was like your mind playing tricks on you. I'm sure it is, unless you're Chinese pal. Then what it is are the mirror people, the mirror kingdom. There's a group of opposites who live in the mirror kingdom and they are sworn to do battle with us. Really? Yeah. And if this were North mythology, we'd lose. Creepy. And we may lose in this case too, but they are in a, I guess, a magical slumber. But when we catch little weird unexplained movement in the corners of mirrors, this is these people

stirring in their sleep, waiting to wake up and kill us all in our sleep. I'll remember that next time I see something in the corner of my eye. Yeah. So that's it for mirrors. That's it. I mean, that is it. Nothing else. There is literally nothing else to say about mirrors. Nope. And if you think that there is, we defy you to go to howstuffworks.com and type mirrors into the search bar, pal. Dare ya. Listener mail time. Listener mail, Josh. This is a little cool organization that we want to support here. And how long have you been smoke free, buddy? It's over four months now. Crazy. Isn't it? So proud. Thanks. Hi, Chuck and Josh. I travel outside the city every weekend, listen to your podcasts and always share my new knowledge with friends. Needless to say, I'm the Friday

night smarty pants and I rather like it. Why I'm writing, I want to promote the New York City Walk to Beat Lung Cancer. I'm one of the head chairpersons at 28 years old. I never thought I would share anything, but I love my new responsibility as I am making a huge difference to an underdog cause. How could cancer be an underdog, Josh? Is that a question? I don't know. I think it's pretty bad. When you hear someone has lung cancer, the first thing that comes to your mind is probably did he or she smoke? It never fails. It is a valid question. Funding for lung cancer is completely dwarfed by other cancers that are nearly as fatal and is completely due to the stigma of a smoker's disease. I get turned away by sponsors and media all the time because no one wants to support a

disease that is so preventable. But the thing is, it isn't. People who get LC second hand for no reason at all happens all the time. Why don't people ask those with skin cancer if they wore sunscreen or people who have heart attacks if they ate well? It's just silly, but looking at the numbers, it just doesn't add up. So here's what we're going to do, Jess, since you were the chair. There's an event in New York City. New York City. It's called the Walk to Beat Lung Cancer. Lung Cancer. And it is October 24th, 2010 in Battery Park. Nice. And if you would like to take part in this Walk to Beat Lung Cancer, Jess would really appreciate it. You can go to a website, www.lungevity.org slash nycwalk. So that is L-U-N-G-E-V-I-T-Y dot org

slash nycwalk. Or Twitter. You can follow this and get information at Walk number four, Lung Cancer. All one word. Or Facebook at Walk to Beat Lung Cancer. And Jess would appreciate your participation. So our New York City buddies that we met while we were there spread the word and get out and walk. Yeah, that's awesome. And if you're one of those people who poo-poo's lung cancer or helping battle lung cancer, yeah, maybe it's time you took a long look in the mirror because you could be a jerk. If you have any kind of organization like Chuck and I to give a shout out to, we consider those on a case-by-case basis, don't we Chuck? We sure do. It definitely doesn't help or it definitely doesn't hurt to grease the wheels. You know what I mean?

And we're not talking about cash prizes. No, we can't legally do that, can we? No. You can tell us about your organization in an email. Just send it to StuffPodcast at HowStuffWorks.com. For more on this and thousands of other topics, visit HowStuffWorks.com. Want more HowStuffWorks? Check out our blogs on the HowStuffWorks.com homepage. Brought to you by the reinvented 2012 Camry. It's ready. Are you? The war on drugs is the excuse our government uses to get away with absolutely insane stuff. Stuff that'll piss you off. The cops, are they just like looting? Are they just like pillaging? They just have way better names for what they call like what we would call a jackmove or being

robbed. They call civil acid. Be sure to listen to the war on drugs on the iHeart Radio app, Apple Podcast or wherever you get your podcasts. Here's today's Fortnite weather report. iHeartland has been hit by a major blizzard. The snow has turned iHeartland and Fortnite into a winter wonderland with new festive games, including a winter themed escape room, a holiday obstacle course, ice skating, hidden holiday gifts and more. Look out for upcoming special events from your favorite artists and podcasters all month, along with scavenger hunts and new how fan are huge challenges. So embrace the holidays at iHeartland in Fortnite. Head to iHeartRadio.com slash iHeartland today.