 This talk and the essence of the talk really tries to get to grips with the underlying principles behind the colour around us and behind the vision that we have and the vision that we use to see that colour. Science such as physics, the interdisciplinary nature of physics with biology and chemistry, it's not dry, it's not static, it's not old, it's new, it's vibrant, it's dynamic. The central aspect of this research work is the discovery aspect. We have been able to do things and understand things and perform experiments. The first people to do those experiments ever in the world, the way that a laser light interacts with a butterfly like this and for the first time in the history of the world, we were able to see that and finally we were able to understand how the mechanism works behind that colour effect. The inner sense really summarises the essence of the thrill. It's adventurous, it means thrill seeking through science. I'm a professor of physics, a doctor of physics at Exeter University in the School of Physics. Some of you are physicists, will be physicists, some of you will be biologists, chemists possibly. All the sciences are linked and the material I'm going to talk to you about today, light essentially, will draw upon ideas and explain concepts in all three sciences, especially physics obviously, because that's what this talk really deals with. But we're going to talk about biological systems like butterflies, like beetles. We're going to talk about the chemistry of colour, of pigments. Science is one big umbrella and to really be a good scientist and to contribute to science, you've got to have a good understanding of all three sorts of sciences. So, there's a lot to talk about. I'm going to rush through things. At the end, there may be some time for questions and you're very welcome to come down and look at some of my demos too. But in the meantime, let's get on. With the first slide, let me try to grab your attention and perhaps you can tell me what is wrong with this image, apart from it being Brittany. Well, let me give you the answer if that was a rhetorical question. Let me give you the answer. The answer is, she's got hair. Okay, that's a kind of pure art answer, that's a cheeky answer. So let's get on to the science. You might look at that and think, that's not science, really. What's he doing showing us a Brittany Spears picture? Well, this actually comes from a science website, Brittany's Guide to Physics. And there's the URL, if you're interested, it actually explains how lasers work in a really clear way, bizarrely. But let me stop you from looking at her. Don't look at Brittany. What's left? Well, what's left is the background behind her. Look at that background. If I were to set you an exam right here and now and say, describe the background, the sort of words I'd be awarding full marks for would be regular, periodic, geometrical. In other words, the holes that you see in that background are regularly spaced from each other. Now, here's the thing. This is a lecture about light, isn't it? About light and color. Here's the link. The link is, if we as scientists could make this, but make the holes very, very small, make them nano-sized apart from each other, then that background would control light. It would manipulate light. And believe me, and I'm going to try to convince you about this today in this lecture, believe me, that is going to affect and is affecting already all our lives. So without further ado, let's get on and do some demos and explain some science. We've got to start with some background. And the background might be is, we've got all this white light behind us. We've got some white light on the side here. We get white light equivalently from the sun. Where do all the colors come from? Well, you look like an intelligent audience. You know the answer already, but let's just revise it in case maybe you were asleep in that lesson. So, how do you separate colors? Well, Newton did this fascinating experiment. He did, took this big glass block similar to this, okay, similar in size, in fact. And he went to his window in the sunny countryside way back in the 17th century. And he went over here and there was a shaft of sunlight coming through his window. He put the prism right on the shaft and it's not very bright outside. And this hole is a bit too big. It's got to be a really tiny hole. And that shaft of sunlight that came through the window went through the prism and the white sunlight, all the colors in that white sunlight separated as they came out through the prism. So, let me dim the lights. Over here we've got all the colors that you recognize. We've got the reds, the greens, the oranges, the blues, the violets. Let me point to a color and you can tell me what that color is. Absolutely right. Well done. Orange, yellow, difficult. Let's try this one. Okay, violet. Yeah, it's all a bit iffy, isn't it? Okay, here's a really tricky question. See how clever you are if I point to this color. Ah, some of you are really clever. In fact, you look at my finger right here and it looks like I'm not pointing to anything. Even though I've said I'm pointing to a color and that's it. The word color. That word color, really, we understand normally in day to day speak as everything we can see across this board at the moment. But believe me, because this slide projector is producing more than just that which we can see, then there's actually more stuff up here. Let me convince you of that or let me try to convince you of that. This is a camera that I bought at a shop on the high street. It's a security camera and this camera can pick up some infrared. So, let me turn it towards the spectrum. Oh, I get out of the way as well. In fact, I'll have to come around this way. So there is the spectrum. Wow, that's really bright. Surely, that spectrum on the board isn't very bright. But when I point the camera towards it, look how bright it is. I'm actually cheating. Look what I'm going to do right now. I'm going to point this towards you guys and then I'm going to take this torch and shine it at the audience. So what we are seeing is actually infrared coming from this torch, illuminating the audience. And the camera, believe it or not, is picking up some infrared. So let's go back to the spectrum over here. Now, I'm going to point to black on the board. Watch where my finger is and then I'm going to point the camera here. So you can see that on the black and white screen, my finger is pointing to some bright light. Whereas here on the board, I'm pointing to black. So where my finger is right now, that is infrared. We just can't see infrared. In fact, let me show you what a serious, a really expensive infrared camera can show us. This is a movie, a very short movie of my friend Ian who works in Exeter. And one winter, in fact last winter, he got into his car and he said, hey Peter, take your infrared movie camera and film me after I've gone for a drive in the car. So that is the engine on Ian's car. Now, here's the special thing. Infrared is actually a measure or can be a measure of the heat of an object, the surface temperature of an object. So look here, that's the car of his engine. And as I start the movie, you can see Ian getting out of his car. It's a cold day. The windscreen is reflecting the ice cold sky above. And Ian's getting out of his car. And Ian hasn't got a lot of hair left. So you can see that the top of his head is losing a lot of heat. In fact, you can see his eyebrows are actually causing him to retain heat in that region. Now, biologically speaking, that's a really fascinating idea. Because that in a sense is proof, absolute proof that mammals, humans who have hair, use that hair largely, or biologically speaking, use that hair to reduce heat loss. That's why it evolved into us, into mammals in the first place. Now, over here, let's just ignore Ian for a second. Over here, we have the spectrum. Now, I've pointed to Infrared. Let me go to the other end. That clearly is violet. And who can tell me what that color is? Ultraviolet. You guys have been well taught. Congratulations to your teacher. Now, what I'm going to have to do is do some demonstrations for you about the use of ultraviolet. Could you guys over here who volunteered, the ladies, could you come down to the front and help me with this demonstration? So, ladies, if you could stand in a line just here, please. Now, what the ladies have agreed to help me with is to demonstrate ultraviolet fluorescent makeup. So let's see if this works. Now, I'm going to have to push you just to that side over there and squeeze by here. OK. So the lamps that we have here are ultraviolet lamps. Can you push back a little bit, ladies? Thank you. Can you see that the ultraviolet is making my shirt, making our shirts glow bright blue? Well, in fact, these little things right here, this is makeup that glows bright yellow or orange or blue when it's exposed to ultraviolet. So I'm just going to, in turn, put a little bit of this makeup on you, if you don't mind. So head back, hair out of your fringe. Do a little bit of this and a bit of that and a bit for you. In fact, let me put it on your hand and you can do it yourself. There you go. And you as well. So I put it right in your nose and smear it right in. Let me do it as well. Here we go. And let's try a little bit of blue as well, shall we, because this is a bit of fun. OK. Just take some of that. A bit of some of that as well there. It's right in the middle of my hand. So industry is actually making some use of this sort of makeup. The way I've applied it clearly isn't perhaps the best way. And the way these ladies who are, I'm sure, much better at applying makeup than I am, they might choose to, and you guys might choose to use this sort of makeup which uses fluorescence. Ultraviolet we can't see. So although we can see a bit of violet coming from these tubes, we can't see the ultraviolet. Now the ultraviolet that is coming from these tubes is pretty safe, so don't worry about that. Normally the UV coming from the sun is harmful, but this isn't harmful. Companies who make this hair gel and companies make this sort of makeup, they are relying on the fact that the dye in this, the pigment in this absorbs ultraviolet and changes it to yellow or to blue or to a wonderful shade of yellow and blue, and then it re-emits it. And that's why we can see these colours. Ladies, you look fantastic. Let's give them a little round of applause. OK. Can you still see all the colour in my face? Not so much. It's bizarre that. If I put this right up here in front of my face, it probably comes back a little bit. So that is fluorescence. Now, back to this. Physics can't stand alone. Biology or chemistry can't stand alone. So let me link in the physics associated with this object, with this shot to the biology, to the evolutionary story. Can you see what we're doing here? We're jumping from pure physics, optics, light, colour to biology. There's a clear link. There's a huge link. So here it is. I've got a friend who works in the reptile house at Bristol Zoo, and he said, Peter, come up to the reptile house, bring your infrared camera, because it's an interesting thing for you to film. So I went up there and I had the camera, and here is a picture taken of me holding one of his snakes in one of these reptile enclosures, and he took this picture. Now, the picture isn't a real colour picture. It's an infrared camera. You can see infrared, obviously. So the picture translates the temperature of the surface of these objects, of my arm, of the snake, to a colour. So let's just decode that. So all the yellow of my hand is around 32, 33 degrees centigrade. That's quite warm. In fact, that is a sign of me getting pretty nervous holding this snake. And do you know why? Because he said, Brian said, this is one of the seven most deadly snakes in the world. So can you see at the far end over here? I've got its head just nice and firmly clamped between my hand because it is a pit viper. Pretty serious stuff. The venom in that can kill a lot of people with just one bite. So let's go back to the biology. Look how hot my arm is. The physics tells us how hot my arm is. But look how cool and calm and collected the snake is. Now do you know why? Why isn't the snake as warm as I am? It's in the same room. It's at the same temperature. I know it's supposed to be cold-blooded, but that doesn't have anything to do with the surface temperature. Here's the reason. Can you see these little pits? In fact, this is why it's called a pit viper. These little pits on the side of its face are infrared detectors. They detect heat, and they detect the heat of its prey. So can you see what's going on here? It thinks that my arm is food. And it is cool and calm because it does not want its body heat to get in the way of it detecting its prey. So that's evolution. If its surface temperature was the same as my arm, if it was yellow under this infrared camera, then it would not be able to detect prey in the same sort of way. Its body temperature would get in the way. So that's evolution. That's called an evolutionary adaptation. And it's really important. We've all got adaptations in ourselves. All the animals in the world have got to where they are today because of their adaptations to evolutionary pressures. So suddenly we're in genetics and biology and evolution, and yet it should be a physics conference. Let's drag it back to physics, shall we? It's all very well, you know? Talking about light and colour, and that's a fascinating field. But to really appreciate it, we have actually got to understand how our eyes see. Here's a fairly cheap model, but nonetheless useful model of a typical human eye. The red sections are cutaway representations of muscle, which move the eye up and down and left and right. So when I take this off, like this, and I'll just put this down, the first thing that I see at the front of the eye is the pupil. The pupil is actually just a hole. And it's a hole, again, which is a wonderful biological adaptation. The hole, as many of you know, the pupil changes size. Let me show you a picture of my three-year-old son's eye. His name is Luke. Luke is three, and I had to persuade him to sit at the desk in my office for me to take this super-close-up picture by feeding him loads of Maltesers. That's kind of bribery. But that eye. In fact, do you know the reason why that iris, why our pupil changes size? About two years ago, I was playing basketball and I got an elbow just accidentally on the side of my head. I was really hurt and my eyesight started to go. So I went to the eye hospital and the doctor said, just sit down. I want to look at your retina at the back. Do you know what the retina is? The retina, once you take the lens out and the glob will fluid out, the retina is what's at the back of the eye. Let me show you a schematic of the retina. There it is, right at the back of the eye here. That's where the light comes through and hits the cells. And our cells, our living cells at the back of our eye, they detect light. So this doctor said, I need to look through your iris, through your pupil and see whether there's any damage. So she said, well, at the moment we're in a dark room. So your pupil has shrunk. I need to add a chemical to your eye that makes it dilate. And she did. And she had a look and after half an hour, everything was fine. And she said, take a few paracetamol off you go. So I went outside and it was a bright summer day and guess what? The chemical was still in my eye. So my eye, my pupil was huge. And I went out and it was bright summer day and it was like someone was hitting me in the eye, someone was putting needles in my eye. The intense light hurt my cells at the back that much. Automatically, if there was no chemical in my eye, my pupil would shrink right down and it would reduce the number of photons, the amount of light coming in. And so it would stop damage in our eye. Now I know many of you have seen this already, but let's do a little test. What I'm going to do in one second is turn the lights right off and then I'll get each of you to look at your nearest partner, your nearest neighbor, really close. And as I turn the lights on, just check out how quickly and how much the pupil gets big again. Can you choose your neighbor? Let's do that. Do you know what that is? That is a biological adaptation. If there are biology, if the way that we evolved, our eyes evolved as humans, if it didn't happen, then our eyes would be limited or we'd damage our eyes much more easily. So once again, we're talking about biology and yet this is a physics lecture. Remember, science is totally interdisciplinary. So, those cells I was talking about, what do they look like? Well, sometimes people donate parts of their body, organs, brains, hearts, eyes to medical research. And this is a picture taken from a lady who donated one of her eyes to medical research. And this is an electron microscope picture of the cells, the living cells at the back of her eye which detect light. Now, it's the lens at the front of the eye which is responsible for focusing light onto those cells, but it's the cells which pick up the light and which change the light energy, the radiant energy into little electrical signals that feed into our brain and our brain then decodes them. So, we've got two sorts of cells, big rods and the rods are responsible for us being able to see at night time under low levels of light, but the color discrimination that we all have, that most of us have, is due to the presence of cones. Now, again at Bristol, a friend of mine works at the vision department there and he says, come up, I've got lots of contacts. He said, come up and let me take a picture of your cones through your retina. And that's actually quite a difficult picture to take because it's not as if you can just stick a camera in front of someone's eye. You've got to use a special camera and a special setup. So, this is what my cones look like. You've guessed it. We see using three different types of cones, cones which are sensitive to red, to green and to blue. In other words, the primary colors of science. Now, art, a lot of you may be artists and doing art, GCSE and art A level and that's fine and that's great for science, but artistic primary colors use a different set compared to scientific primary colors. So, here we go. Three primary colors, three color photoreceptors. Receptors, receivers of photons and photons are particles of light. Now, what happens, here's a big question, what happens if genetically we have inherited a gene which has a little tweak on it, which is slightly different and what happens causes us to maybe have a different sort of photoreceptor, here. The answer is, you see color in a different way. Now, the traditional name for that sort of condition is color blindness, but I have to say right now no one is blind unless it's a really serious form of that condition, but someone who has a different color genetic workup of their photoreceptors, they are not blind. They just see the world in a slightly different color light. Now, some of you may have this color alternative version of the world, let's see who has, maybe. This is a really simple eye test. Please don't shout out. Please don't shout out, but can you see, can you identify the three color shapes? Don't shout out. You chaps up there. Okay, let me give it away. So, right here. My eyes are not perfect. Don't get me wrong, okay? So, that is a kind of mustardy yellow square. Everyone see it? Good man. That is an orangey creamy brown. Well, it should be a circle. Fine, everyone see it? Good stuff. Okay, just in here, and again, my eyes aren't proper perfect. In here is a kind of slight bluey-greeny vertex of a triangle coming down, just skirt in the top of that line to about here. You can see that? Can you see it? Because I've got a... You've got super woman vision. Fantastic, because I'm just making that up. Okay, that was just a little trick. Now, there are only two objects. Only two objects. But, this is a silly test, because it's not a proper test. It's not a proper recognized medical optical test. Those tests are called the Ishihara tests, and they're named after a Japanese professor of color vision way back at the turn of the previous century, who came up with standards. You shouldn't just recognize squares or circles or shapes of objects. You've got to recognize, generally, be able to recognize or differentiate numbers or letters. Now, here's the proper test. Don't shout out the number. That's a two or a five. Don't shout out. That's a 29 or a 70. That's a 74 or a 21, and that's an eight or a three. Now, many people with color standard vision will be able to distinguish both numbers, either number. But some people who have a color alternative sort of vision can only distinguish one. So, for instance, most people here, who can distinguish a five? Well done. Up here, who can distinguish a 70? Good, because it's a 29. Who can distinguish here a 21? I can sort of see a 21. There's a sort of bottom of the two. There's a one here. But the proper number for color standard, the dominant number would be 74. And over here, again, it's an eight. So there may be some of you who can only see one and perhaps you're a bit shy to put your hand up. It does not affect your life, except in a really extreme medical case, and you probably wouldn't be here if it was that extreme. Color alternative vision is just something that your brain adapts to, and it doesn't make you any better. It doesn't make you equip you with better eyes or worse eyes. It just allows you, in fact, to see the color in a unique way, slightly different to other people. Now, genetically, here we go with biology again. Genetically, get this. One in 10 men have color alternative vision, but one in 250 women have color alternative vision. Now, what's that all about? To answer that question, you've got to turn to genetics. You've got to realize that this color alternative vision is due to a specific tweak on a gene within the X chromosome. Men are XY, women are XX, so if a man inherits from his maternal side an X chromosome that has that color alternative tweak, he will definitely be color alternative. But if a woman inherits a color alternative X, she may also have her second X, because she's XX, will be color standard, and that's usually the dominant gene. And so her, she will be a carrier of this color alternative vision. Now, we're going on rabbit and on. We're going on a biology again. It's such an interdisciplinary subject. Let's get back on track. How do we produce color? Now, I've shown you that if we use one of these things right here, a prism, we can separate the color from white light. Great, okay, that's a classic experiment. But my hair, well, my hair used to be really dark. I used to be really proud of it. But it's gray now. Your hair or skin or eyes, whether it's dark or light, that depends on something inside it called melanin. It's a pigment. Some people have red hair. That's due to a different pigment. My gray hair is because I don't have very much dark pigment, melanin in my hair anymore, okay? So melanin is a pigment. One of the ways of producing color, this first way, is a pigmentary color through dyes or through pigments. And we could go into the chemistry of this. Suddenly, we're on to chemistry, okay? What is this? We won't go into a lot of detail. The chemistry relies on a molecule. Now, let's see how good a chemistry you guys are. What is the name of this molecule? Let me give you a clue. Remember, we're talking about color. What color, what molecule, what pigment is responsible for that green right there? Chlorophyll. Well done, that was a unanimous chlorophyll from all three sections. Fantastic. We have three pigments like melanin. In fact, let me show you what chlorophyll looks like color-wise. So we have three pigments there. The green one is chlorophyll that I've extracted from the top of some organic carrots from the sort of leaves of organic carrots, okay? And that extraction is quite difficult, but it's possible. Chlorophyll is green because, well, let's see why it's green. Why is chlorophyll green? When we shine white light at it, now, up here, I am representing white light, sunlight, if you like, as a combination of three primaries, so red, green and blue. What happens to the red and the blue? That's the real question. The question isn't just, okay, why is green reflected or scattered or whatever word you want to use. The real question is what happens to the red and the blue? Does anyone know the answer? It's absorbed. Wow, your teachers must be fantastic. It's absorbed. It's absorbed. So pigments work through absorption. Let's talk about the other pigments. That's chlorophyll. That is blueberry juice. And that, well, I could be really disgusting. And I could say, you know, I used to have a little dog and unfortunately she died. But before she died, I was able to take some blood out of her. And that's not true. Right now, that's not true. But that word, blood, normally we associate blood with a living process, with life. Because blood takes oxygen from our lungs and distributes it to our cells. Now, that could easily be blood. It is not. Because blood, the name of red blood, is oxygenated hemoglobin. That is just a pigment. Even though it's vital for our lives, for life, it is just a pigment. Now, let's see. Do you know what vegetable it's from? Beetroot. That's beetroot juice. Again, it's just a pigment. Now, here's the thing that I really want to demonstrate. This is the real physics, the biochemistry and physics of it all. How do these things work? What do we get when we color mix? Many of you might be artists and you might do art all the time and you mix your pigments and mix your paints. What happens when you mix green with red or blue with red? When you work by absorption, then a funny thing happens. Let's see, shall we? Green is green because it absorbs red and blue. Red is red because it absorbs green and blue. Keep up with me. Blue is blue because it absorbs red and green. Red and green. That absorption is going everywhere. So if I mix all three primary pigments together, primary pigments, then the absorptions will all cross over and overlap and everything should absorb everything. Shall we see if that's the case? What happens to light if everything is absorbed? What have we got left with? Black. So let's do that. And there it is. That's pretty black to me. Remember, that is black. Pigments mix in a color subtractive way because of the absorption color is subtracted out of the overall effect. And that's an important thing to remember. Really important. Okay, let's move back. Lies and absorption. There we go. So the second way, and this is the really important way, guys, I know we've probably spent half the lecture already talking about pigments, talking about things which are interesting but are not really fascinating. Let me try to really fascinate you now if I can. And I can tell all of you are seriously fascinated already and I'm gratified to see that. Okay, soap bubbles. Soap bubbles. You smell like a clean audience, which means you take showers very frequently and it's great. And when you take showers, you use soap. And when you use soap under water or with water, you get bubbles. And soap bubbles just like that. Soap bubbles are colored. If you look closely enough, if you put a black background behind them and illuminate them with some sort of white light, you will get some wonderful, deep, saturated colors just like that. But you've got to look carefully. Okay, you've got to look really carefully. Now, soap solution. Even if it's, even if fairy liquid is a little bit green, I know it's green when it's right in the bottle, but when you dilute it down, it's transparent. How on earth are we getting all of these beautiful, deep, deep colors out of something which has no pigment in it, which is not colored? Which is really not very far away from water. That's what we have to investigate, okay? There is a mechanism responsible for that. And that mechanism produces the colors in all of these types of animals. It's not structural color because it's the structure of the thing. It's the thickness of the layers which create the right conditions for bright colors. Now, let me show you some of those colors. Here's a picture at our local lake that my five-year-old daughter took. Lovely ducks. And here's a peacock. You all recognize that the blue that we see here is a bright, bright blue. It's a much brighter blue than you will ever get from pigments. But it's incomparable compared to this sort of blue feather. It's amazing color. In fact, let's just show you some of the color in one of these butterflies. If I flick through to all these different plants and beetles and butterflies, let me show you this. Do you see that butterfly? Now that has no blue pigment in it whatsoever. All of these colors that we see here, the greens, the the greens, the blues here, the little blue spots, all of those colors do not have blue pigment or green pigment in them. They're produced in the same way that the color of soap films produce color. Can you see the clown's face on here, by the way? Have a really close look. Let me keep asking the question. Can you see the clown's face? That's a clown beetle. The real question is, in terms of physics, and remember, we're back on the physics track now, in terms of physics, what on earth is going on? What is the underlying principle that produces that color? We're going to have to show you a picture, and then we'll do a demonstration right here. There's the picture. On the left, we have two waves which have their peaks overlying, one peak on top of another, and when you add them together, they produce a super peak. But when on the right, you displace, you move one peak a little bit so that it's overlying a trough, then you get cancellation, the condition, the mechanism is called interference. That's a word you'll have to know at A-levels, definitely. And it can be constructive or it can be a super wave or a super peak, or it can be destructed. Aaron, may I ask for your help if you can stand there? Ben, may I ask for your help? Can you stand over there? What we're going to do is demonstrate that. Give the boys a little round of applause for coming down. Right, Ben, if you can hold that in pretty tightly. Go right as far as you can over there. Actually, come forward and hold just before the knot. That's it. Aaron, go right back, go right back. Go as far as you can slightly to your right and back a little bit further. Back a little bit further, please, Ben. Perfect. Now this thing could be a skipping rope. We could get a skipping rope thing going, but what we're going to use it to represent is light. Is light travelling between two places? So over here, on Aaron's hand, I'm going to send a pulse of light, a light wave down this medium towards Ben. Watch this. Actually, go right back to the seat. Fantastic. So here is the light pulse. Now tell me, everyone, look closely. Tell me what happens when the light wave meets Ben's hand. So here's my pulse. I'm winding up. What happens when it meets Ben's hand? It reflects absolutely. Now what I could do is instead of sending just one pulse down, I could keep going. I could keep tweaking it at a constant frequency. And what you will see is that the wave going down here will meet the wave that went before it that's coming back. So we've got two waves. We have the addition of waves. Now if we get it right, if we get that repetition rate, that repetition frequency right, then the peak of the wave coming down might meet the peak of the next wave coming back and what we have is two peaks or two troughs adding right in the middle. Aaron, can you just sort of tweak your hand regularly? Little bit more slowly. Exactly like that. Keep it going. Now this might look like a skipping rope. Bit more energy. Well, bit more energy. Excellent. Excellent. Raise your hands up a little bit. Bit more energy. Now that might look like a skipping rope but what you are witnessing is interference. The peak going here is constructively interfering with the peak that's coming back. Excellent. Now we're going to stop you there. Let's try to get destructive interference right here in the middle. You keep your hand still Aaron. Ben, I'm going to ask you to do it. Can you waggle your hand slightly faster than that which Aaron used? I'm going to just stop you. Kick in with a fast one straight away. Sometimes you fall into the same frequency. Let me just start you off and then you can take over. Can you do that? It's tricky. It is really tricky. Actually if we go in a circle then it's a bit easier in a circle. This is so hard. I'll tell you what, go as fast as you can. Ben is doing a great job here. Can you all see that occasionally we're getting zero displacement in places? Right here, there's a zero displacement. That means there's destructive interference going on in this place. Big one. Can we please give these fine gentlemen a round of applause? Thank you Ben. Cheers Aaron. That in a way is how colour is produced but let's really see how colour is produced. What we need is a film or a little structure. Here's our structure like a soap film and we shine white light down on this soap film. That's what we have to have. It comes down at a particular angle. It can be a straight on or it can be a large angle. Let's vary that in a minute. Now when we get a reflection from the top we also get a reflection from the bottom and suddenly this is the important bit. Suddenly we've got two waves of light. And do you remember what light waves do? They can add together destructively or constructively. Remember, the angle is really important. Now let me show you exactly how important the angle is. Here's a little movie. What colour is the car? Have a look at the side of the car right here. What colour is it? Red. Pink. Red. Pink. What colour is it? Keep archery. Keep archery. More, more. What colour is it? What colour is it? So if you're driving this car and let's say you go a little bit too fast or you're kind of you're wavering. Let's say a policeman stops you and the policeman says, is this your car, sir? Or about it? And you say, yeah, you love it. And then he or she will say what colour is it? Well, it was pink. The answer is, the correct answer is it depends on the angle officer. Because, because as you saw, the colour changes and that is the definition of an iridescent colour. Now you can't get an iridescent colour through melanin or chlorophyll or cyanine or anything like that. You can only get it when you use tiny little structures to create the colours. So, butterflies have been doing that for a long time. And as scientists, we studied this butterfly and about eight years ago we sat down at the desk, a few of us at Exis and we thought, we're physicists. Let's ask a proper physics question. How is the blue produced? Some of you might do an experiment like that and your teachers might say, tell me how this is done and you've got to do a measurement. So we did all our measurements and then like proper scientists, we try to be proper scientists, guess what we had to do? We had to write our results up into a report, an experimental write-up and we put a title, an introduction, a methods, a result, a discussion, a references and then we published it. And here are some of the things that we discovered. Let me show you. When we looked at the wing using an optical microscope, we saw all these things. And in fact what I've done is I've brought an optical microscope here and it's a bit of a low-tech one but nonetheless we should still be able to see the images from it. Now I'm going to have to dim the lights for this. Temporarily there they are. There are the butterfly scales that we saw about eight years ago. So if I can focus a bit or move them around a bit they're out of focus, let me focus them up. There is a scale. There's a scale right there. There are lots of other scales. This is a region where the scales are missing. And that's exactly what we saw when we did this experiment a few years ago. But that's not enough. That is absolutely not enough because you have to look with more detail and to do that we need an electron microscope. So now we've got some images taken using the electron microscope. And these microscopes are great. They're fantastic. They don't use light because sometimes it limits the detail that you can see. You can only get to a certain magnification using a light microscope. Whereas with electrons you can get really massive magnification. So that's a good magnification. That line there is one millimeter. So think on your finger how big one millimeter is. And then think even further how big one of these scales are. There's one scale. And when we look in a lot of detail at the scale look what we see. These parallel lines up and down but also you've got to have a really careful physicist-scientist eye on. Have a look just in here. There are some tiny little layers. And it is those layers which are responsible for creating this blue reflection. Without that it wouldn't be blue. Now we published, we wrote that up and we published it in a journal. And then that journal went all over the world in the normal way. Not necessarily anything special but it was just in a normal way. People can read that. Guess who read it? L'Oreal read it. The L'Oreal Cosmetics labs the scientific labs in Paris read that. And so they gave me a call and they said come over and present your work to our scientists because it's the idea of being able to produce color without pigments and applying that to makeup that we want to try to use. And that's the nature and apply it to our technology. And so they made some makeup. They made some photonic cosmetics. That word photonic again, it's a special word it involves using light using photons of light. So there is some lipstick. It's got no red pigment or no blue pigment in it but that blue sheen is the result of an iridescent effect just like the car body. Now when we zoom in and see these big huge lips right there you might think oh that's a bit garish that's too much for me. Maybe Western Europe isn't ready enough isn't ready yet for that. You'd be right maybe. It's not fashionable here yet. In fact if you look at anything that close up on someone's body it doesn't look all that appealing. But when you take a step back and look at the model admittedly she's an attractive lady but when you look at the model professionally made up the look, the makeup is a very demure very elegant look to it. I wish some of the inspiration was taken and there's me on the side a L'Oreal model or as close to one as I'll ever get. So there is an application of some of these ideas. A group of scientists admittedly from Exeter, from us at Exeter we studied this natural system and we applied those ideas and we helped other people apply them to technology, to industry. Let me jump ship now to turn the subject around. It's not blue, it's now green and we're actually not going to talk about a butterfly for two more minutes until we talk about neo-impressionism. Who painted that picture? Sura. Who can tell me this? What is special about that painting? God. Dots, absolutely. Do you know what other kind of really posh word we use to describe painting with dots? Points. They're dots, they're points of mentalism. In fact, this picture is made up of tens of thousands, hundreds of thousands of microscopic little dots. So this artist, this is a huge picture in this artist, you know what he did? He had the big canvas in front of him and all he did was just get a tiny little brush sharpen the end, dip it into a colour dotted on the board dip it into the colour dotted on the board for eight years. But it's worth. I don't know how much it's worth now, but it's a fantastic piece. Now, you can't really see all the tiny dots because they're so small but let me show you the effect. Here's the effect. That's like a normal picture. You can sort of see some dots but let's zoom in. Suddenly, you can see now that all the yellow region is made up of dots. All of this region down here, they're tiny little dots of colour, different colours. Now, why? That's a good question. Why on earth did he choose to do that? Well, here's the reason. We've got a different sort of colour audition. Colour addition. Anjali, can I ask you just to step up to the control box over there? Now, what this young lady is going to help me do is to turn on some coloured lights. Let me turn the main lights off. So, first of all, could you flick on red temporarily and then blue and then green? Red, red off. Blue or green on. And then the last one, please. What we're going to do is we're going to add big dots of colour. These dots are now massive. All three on at the same time, please. Suddenly, we are now mixing projected colours. Look at this. So now when all three primary colours, red, green and blue, overlap in the middle, we've got white. Now, hey, wait a second, you shouldn't be saying, you should be saying that white you're telling us about in the middle. That's not a good white. That's not a proper white. Look at it. It's a sort of ready white. And you'd be right. You'd be absolutely right. So what we're going to do, because it's a ready white, we're going to turn down red a little bit. Could you do that, please, Anjali? Just turn down red ever so slightly. Turn it off, actually. And bring it up slowly. Bring it up. Keep going, keep going, keep going, keep going, keep going, keep going. Stop. That looks like a slightly better red. So what we're getting at is if you mix colours, projected colours in the right intensities, you can get any colour you like. How do we get black this way? That's right. Turn all the colours off. Please turn them off if you would. And let's give our wonderful assistant a little round of applause right there. Thank you very much. So, you might think I've never seen this before, but you have. You've seen it every single day, probably of your lives, except maybe one or two days on holiday when you work near a colour television. Colour televisions produce all their gamut of colours, their range of colours by mixing three primary colours. Your colour mobile phones are colour game consoles. They mix little pixels, little points of colour for all three different colours. That colour mixing is different. We call that additive colour mixing. It works in a different way to the subtractive colour mixing. The mixing by absorption that we've got here. And that's, you've got to bear that in mind when you think about art, when you think about science. They're very different in those two different addition systems. So, why on earth did we talk about that? Well, let me show you why. Here's a beautiful butterfly right here. This is a Papilio butterfly. And let's run the movie. There it is. This is my favourite butterfly of all time. That green, biologically speaking, that green is a camouflage green. So it has evolved the green in order to camouflage itself against the leaves on which it sits and on which it lays eggs. But how is the green produced? Well, when we take a picture of it, let's take a big picture of it. There it is. Have a look using an electron microscope what the scales look like and the scales look like this. Normal sorts of scales. Now I said that this microscope here is a little bit iffy, but nonetheless it will still give us an indication about what colour the scales look. We expect them to look green, don't we? Let's turn the lights off and let's go back over here to have a look at the Papilio butterfly. What I'd like to ask you is where is the green? Now this is a green butterfly. But where is the green? All I can see and I think all that you can see is lots of yellow and in between the yellow there's lots of blue. When you take a picture using a proper advanced microscope, guess what we see? This is what we see. That is the colour that we see. It's a mixture of blues and yellows. And do you know what colour we get when we mix blues and yellows? We get green. So in other words this butterfly has evolved the ability to make green using two different colours. It uses that pointillism that pointillistic colour mixing effect and it invented it it evolved it 50 million years ago and that French guy who invented as it were neo-impressionism he invented his painting technique around 100 or so years ago. Figure that. We're actually using these ideas. We did this experiment and we published these results and guess who decided to use it? Well the anti-counterfeiting industry is in the process of using these ideas. Every single year this is a fact. Every single year the people who make anti-counterfeiting logos on credit cards or on banknotes or on theatre tickets or on software packaging they are only six months ahead of the counterfeiters. So the industry is always looking for ways to make logos, ways to make complicated colourful logos that are really hard to replicate and reproduce and believe it or not the ideas that we and others have discovered in this butterfly are being used, are being mimicked. We don't, these butterflies aren't killed and then put in the credit cards. No, the ideas are being used. That's the important thing. All world ideas are being copied. So we've got a couple of examples already. Now we've just got a few more slides and then the lecture is nearly over but we've got one amazing bit of physics and an amazing application to come. This will affect all of our futures in the next 15 or 20 years. Let me try to introduce it. 3D photonic structures that's a fancy complicated phrase. 3D stands for three dimensions. Let me show you a three-dimensional object. Well, everything, all of us are three-dimensional obviously but let me break it down a bit. These are three-dimensional models of chemical crystals, of crystals. This is a model, it's a cubic 3D model of sodium chloride with the green atoms representing sodium ions and the gold atoms or spheres representing chlorine atoms. This is a different sort of 3D model that represents diamond. It's a tetrahedral structure and each black sphere represents a carbon atom. Now, whatever way I turn it, it's three-dimensional. It offers a different surface to us. Here's an amazing thing. Have a look at this beetle or at these beetles right here. Bearing in mind what I've said about that 3D set of structures, have a look at this. There are some wonderful friends of mine and you saw a few on the desk on the visualizer right here. That blue one is in particular very interesting. Let's examine it. Let's do our normal set of physics analysis experiments on it. That involves using an optical microscope and an electron microscope and lots of other things, of course. So let me show you the electron microscope images. Here is one image of a scale, a region of the wing. So there's, we're taking a region of the wing just here. There. These are like our hairs. In fact you can see some longer hairs there. If we plucked out one of our hairs from our heads and had a look at it, it would have a root and that root sits in our scalp. These scales each have a root. You can just see the root right there and that sits in the wing substrate of the beetle. Let's zoom in. There is one scale. Now, there's no scale bar on that picture but let me put it into context. This is amazing. This is so small. If we had this in our finger we wouldn't see it with our eye microscope or a magnifying glass. If I plucked out one of the hairs in my head and cut the end off so that the end was actually a circle and then if I put that end in the electron microscope just like that one, well, one end of its diameter of my hair would start here and the other end would keep going way over to about there. About the end of that bar right there. That's how big this is relative to a hair in our head. So let's keep having a look. Let's examine. Let's be proper scientists. Let's examine what's inside. What we did then is we broke open half of that scale to see what was producing this blue color and lo and behold when we zoomed in we saw that it was a three dimensional structure. In other words the beetle right here the beetle scale has evolved this type of structure but the size between the spheres between the points in the three dimensional structure is exactly the right size to create a blue reflection. To manipulate blue light. That's what we're doing. That's what the beetle is doing. It is controlling and manipulating color. Now imagine if we copied this three dimensional structure. If we copied it in three dimensions guess what we could do. We, you would have the ability to create light completely in all directions. In that direction. In that direction. In that direction. In all three dimensions. And that is actually vitally important. You might think okay fair enough. Cosmetics. Not very useful to the world. You might think car paint. House paint. Not very useful to the world. You might think paper. You might think fashion fabrics. In fact I've got some fashion fabric over here that you might like to have a look at a little bit later on. It's a mimic of the butterfly and it's a wonderful blue color material. Not very useful for the world. You might say. But I'll tell you what is useful. Being able to manipulate light in all three dimensions. Using these sorts of three dimensional structures leads to a potential application in computers. So here is my old computer. Here is one of the processing tools from the old computer. There. And in fact let me put it on the visualizer. There is a processor. Light on. That processor is one of the processors that does all the work. When you play your games. When you do your web surfing. When you write your projects up. When you search for images. It's that processor amongst others which is really doing the crunching. Doing the processing. But it's slow. The reason. The reasons you might know and you might understand. Let's have a look. If we have a look at one of those chips. Put it on our finger. And then if we prize open the top of the chip. Guess what we see inside. We see this. Array. This complex jungle of electrical components and wires. Now the electrical components are the physics of them. The science of them is really complicated. But it's well known. But they're resistors, capacitors, transistors. Lots of things which allow signals to go from one transistor to another. To do the processing. To do the networking of communication really. But the main content of that chip. Of that board is this. Let's zoom in. There it is. It's wires. There are hundreds of thousands of wires on this region right here. What's the problem with electrical wires? Let me tell you. Let me tell you the problem with electrical wires. They have resistance. You know about electrical resistance. You know about Ohm's law possibly. When you put an electrical current. When you try to flow electrons through a wire. The electrons make the wire heat up. So the electrical energy you use to do that part of it is converted into heat and it's wasted. So the computers get hot. The chips have to be cooled. That's a huge waste of energy of natural resources. Not good. But worse than that. Worse than that is the fact that electric current. Even if it's the electric current in these processor wires. It travels really slowly. Now it's far faster. If you stand at the edge of a room and flick a switch to turn the lights on. The lights come on within milliseconds and you might think wow. That's fast. But really in the grand scheme of things it's not fast at all. It's really slow. What is? Tell me this everyone. What's the fastest thing in the universe? The speed of light. Light traveling from one point to another point. With no air or no solid or no glass in between. Just vacuum. Just space. That light travels at the fastest speed. Now even if light travels through air. That's still pretty fast. So get this. What if we take away the electrical wires. And we replace them with light wires. I'm not talking about optical fibres. We've moved on a little bit from those. Even though those are sort of light wires. We're talking about something else. We're talking about photonic crystals. Crystals just like this that the beetle has shown us. Either in three dimensions or in two dimensions. Which allow us to manipulate light to send communication signals back and forward between transistors within processing chips. That will completely revolutionise computer processing. Communication. Signal processing. And that will happen in the next 15 or 20 years. So guys in the States and this is from Boston. From MIT I believe. Guys are modelling these things. Before you build things like this. You have to demonstrate that they work using computer models. So do you remember that background behind Brittany right at the beginning. That I said was useful. That I said if you make it the right way. Would manipulate light. Well here it is. And there is a little area where the holes have been removed. And when you press your button or when you hit the return key on your future computer. That will set a few light signals going. In lasers. In light emitting diodes. And those lasers will communicate from one place to another place via a light path. A light guide. So let's press that button. Watch me. We're going to press the button. Up here. And the laser will fire. And there is the light. Going around corners. And it's travelling around corners via this effect called interference. It's a lot more complicated a system. Now it's like a two dimensional or a three dimensional type of system. But light can go around corners. And up or down or across or backwards or forwards. Any way you want it. If you can control. And if you can manipulate light. Now it's not just the natural world like beetles and animals that are teaching us how to do that. Scientists, you know male professors, female professors, all these technicians, all these post docs and post grads. Men and women. Don't forget loads and loads of women are in this photonics industry. Previously physics was limited to male and sort of stuffy but now some dynamic and bright young women are enthused and are pursuing these goals. It's a noble goal applying the ideas of natural systems to the physical, to the real world, to the industrial or technological world. Now okay, that's come to the end of my diatribe. But let me leave you with this movie. And with this movie I'd like you to maybe leave afterwards with a sense of hey maybe this beetle or this ant or this spider that's walking across my hand or whatever it is. Maybe there's more to it than meets the eye. If I could somehow magnify my insight into its internal structure what would I see? In the bottom right is the magnification. Look a butterfly. This one comes from Madagascar. Its bright colouring is as much a call for attention as a warning. It follows the weather changing along with the lighting responding in time to both shadows and light. It's iridescent. As we move closer the features that give it this characteristic are unraveled. On the surface of the wing we can see two layers of folds. Light and fragile looking it's hard to imagine that they're indispensable to the flight of a butterfly. Underneath the folds which cover each wing are black. Their colour is due to melanin a pigment responsible in the human body for the suntan and the colour of the hair. The black coat emphasises the contrast with the top layer enabling the iridescent folds to stand out in the dark background. There's no pigment in these coloured folds though they have no specific colour. Actually there can be any colour depending on the angle from which they're lit or looked at. When going through the folds the light is decomposed. When reflected back to our eyes it's iridescent of all the colours of the rainbow. Magnified 2,000 times here is the reason for the iridescence. This white braid constitutes the broken edge of a fold. A membrane a black and grey plaque visible underneath. Appearing in grey is chitin a series of long sugar chains. What we see in black is only air an empty layer of air. This provides rigidity, lightness and colour to the whole structure. The rays of light going through this system are much of the structure's inner walls and intertwine as they would on a soap bubble. They send back those iridescent colours characteristic of the wing of a butterfly. Our microscope has now unfortunately reached its limits. Beyond this nothing more is visible for the moment. So this has been light fantastic and you've been a great audience. Thank you.