Illuminating Light - Jess Wade, Russell Foster and Bridget Christie

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0:35BBC Sounds. Music, radio, podcasts. Hello, I'm Brian Cox. I'm Robert Ince and this is the Infinite Monkey Cage. Now, the process of science was once described as a man dropping his keys in the dark but then crossing the road and looking for them under a street lamp because that's where the light is. It's just complete dribble, isn't it? Who said that? Noam Chomsky. And what was his expertise? He's a linguist and street lamp mender. Today we're asking how has the availability of light changed our culture and our understanding of the universe? How does light affect the rhythm of our lives and indeed the stretch of our bodies?

1:13And what is light anyway? To help us understand light, we are joined by a circadian neuroscientist, a ramen spectroscopist and an existential biker. And they are.

1:25Russell Foster:Russell Foster. I'm the director of the Sleep and Circadian Neuroscience Institute. And I've spent a big chunk of my life trying to understand how light is detected and how it regulates lots of different parts of our biology, but particularly how light is regulating circadian rhythms and sleep. And what about light makes me happy? Well, it's something I will be completely unaware of because it's the exposure to morning light that will set my internal body clock and my sleep-wake cycle, which will synchronize my rhythms and allow me to do what I need to do most effectively, and that will make me very happy.

2:03Hi, I'm Jess Wade. I'm a research fellow at Imperial in the Department of Materials, and I study and kind of work on atoms and molecules and how they absorb and emit light, and particularly how we can think about using that for creating new technologies, whether that's kind of light emitters for displays or solar panels, so things that can absorb light and generate electricity. The thing that most enchants me about light actually is when we start to look at nature and try and understand how nature controls and emits or absorbs light and then try and replicate that in the lab to create these new technologies.

2:37So there are these particular types of beetles called jewel beetles that have these kind of beautiful iridescent shells, so they sparkle when you look at them from all different kinds of angles. and that's actually because the kind of materials inside their structure are arranged in this particular type of nanostructure such that when light shines on the top of them, they reflect light that's twisted. And our eyes can't tell whether something's twisted left or right-handed because they're not that sophisticated. But if you have 3D cinema glasses, which weirdly are that sophisticated, you can see this really beautiful colour through one of those lenses and no colour at all through the other lens.

3:11So it's just this kind of miraculous, clever way nature's created this quite sophisticated nanotechnology that we try and then emulate in the lab to make the technologies that we use in our human lives better. And I find that kind of completely magical. Yes!

3:32Well, I'm Bridget Christie and I'm a comedian. And the light that I find most magical is, you know, when, like, you go into a room and it's dark and you put a light on and then you can see things. And this is our panel.

3:55Can I just ask, when you were talking there about the left hand or the right hand of the spiral there, because I'd never realised Ursula Le Guin's book Left Hand of Darkness. So could you just explain the left hand and the right hand thing? Well, about kind of, particularly in light. So it's this kind of concept of chirality. It's actually what I study most in the research that I do. But chirality comes from the Greek word for hand. And it's kind of this idea that you get objects that exist as non-superimposable mirror image pairs. And that's a kind of fancy way of saying they have a handedness.

4:22So your hands, if you put them together palm to palm are mirror images. If you put one on top of the other, there's no way you can rotate your top hand to be a mirror image of your bottom hand. And we see it in kind of subatomic things like photons, packets of light and electrons. we see it in molecules particularly biomolecules actually proteins and dna and we see it in macroscopic things like gigantic things like galaxies so actually that twist of light is a really really interesting phenomenon because it lets us study loads of biological processes but actually harnessing that twisted light lets us do lots of new things for technology and there's still so much to understand about it it's really interesting area to work in um what gcse's did you do probably the same ones as you i didn't do any okay i did i did a few more than that in that description russell we're already there talking about light as a thing with a rather complex structure and behaviors but historically speaking when do we start to think of light

5:22Russell Foster:as a thing as something that can be explored i think pretty early on i think we've always had a wonder about light. If we think about the great religions, they all have light at some level at their core. Of course, during the Enlightenment, hence the name, we began to study it scientifically and became aware that, of course, it allows us to see. It's fascinating in terms of vision. The original ideas from the ancient Greeks was that it was light from the eye that bathed objects, and that allowed us to see. And even Leonardo da Vinci thought about that for a while. So our understanding that it's light reflected off of objects into the eye that allow us to see is a relatively late phenomenon.

6:06I never understood that. Because as you said, Bridget, you go into your room and turn the light on. How did Leonardo da Vinci not figure out... He didn't have a light switch. ..that the light is not coming out? I suppose this is one of his business subjects. Why did you not invent the light switch? It seems obvious that you can go into a dark room and you can't see anything. Am I missing something?

6:30Russell Foster:I think it's because the ancient Greeks had such a pervasive sort of view on science and medicine that it was kind of just adopted. And it was only later when people started to become critical and ask, well, hang on, is that quite right, that the whole thing started to unfold. Bridget? Well, I don't know if anyone knows this, but the light that everybody sees when they have near-death experiences, whether you believe in those or not, but everyone talks about this light. and I was just wondering if anyone knew why that happens. Some people say it's almost like the mind shutting down. So you remember the old television sets?

7:04Yes. Where it's almost like everything... I'm afraid it's time for closed down, by which I mean you're going to die. And so it was almost like the shrinking of a visual field. There's a lovely film all about this elderly choir. It's a documentary. And at one point, one of the choir was very, very ill and they thought he was going to die. And the quarrel master goes, some of you have nearly died as well, haven't you? Barb, you've nearly died. He goes, yeah, I did nearly die. I didn't like you. Go, Michelle, you've nearly died, haven't you? Yes, I did. And he goes, Daisy, you did die, didn't you?

7:35And she goes, yes, I did. I was dead for two minutes. He goes, did you see the light? And she goes, I didn't look. And I thought that was the most beautiful thing. But I wonder, yeah, that's an interesting... Why that sense of the shrinking?

7:51Russell Foster:Well, I'm guessing. But the eye, the retina, has the highest metabolic rate of any tissue weight for weight. And so if you are losing levels of blood oxygen, then the whole of the visual system is going to slowly shut down. And people who've had a stroke describe exactly that thing, where their image of the world essentially goes to a dot and then disappears. From a scientific perspective then, so light is part of our culture throughout recorded history. Jess, you referred to light as a stream of photons. so so could you talk us through that progress of several centuries from thinking that light is a wavy thing you put it through lenses and we understand how it behaves and then we start talking about it in terms of particles which is as you described it yeah about early 1000s there was quite a lot of work in the islamic golden age to really understand light long before actually we're looking at it in the western world there was a bunch of physicists ibn al-haythan who who really defined this kind of optical geometry and actually built the first camera obscura to be able to look at it.

8:51So had predictions and understandings about reflection and refraction and, you know, how light interacts with surfaces or passes through different materials. And then until about 1500, people started playing around with lenses and optical components and things like that. And then through that 1400s, 1500s, 1600s, people had become obsessed with trying to define what light was. So you had these competing theories. You had Newton, who's playing around with his prisms and shining light on them and getting these rainbows and explaining all these beautiful things about colours, but still thinking it was particle-like.

9:23You had Christian Huygens saying it was a wave-like nature. No one really wanted to offend Newton. So there's this kind of constant conversation where scientists were saying one thing and then trying to argue it and debate it. But then pretty conclusively, Thomas Young showed in 1800 this kind of two-slit experiment and showed that if you shone light at two slits, you got an interference pattern. So this adding up of light waves and subtracting this constructive and destructive patches of interference, these bright and dark bands on a screen behind that you couldn't get if you had a stream of particles going to these two slits.

9:54So this is a massive thing. It was in London. He showed it at the Royal Institution. So that was 1800s. Everyone was then convinced, okay, light's a wave. And then 100 years later, Einstein and his quantum friends came along and said, actually, light also has this particle-like nature, and they did these experiments of the photoelectric effect, and then we came to understand that both electrons and photons had this wave particle-like nature. So you went from saying it's a particle to it's a wave to, oh, no, we're happy with it being both. And now we harness, actually, we think about using both the particle and wave-like nature of light to create technologies to understand the world and the universe.

10:29Yes, we see that's a beautiful... APPLAUSE I was just... I don't know if you've seen it. There's a cat on Instagram. And, no, it's kind of psyching itself out because it's looking in a mirror at itself and it thinks it's another cat. But I was just wondering if we know when the first human saw a reflection of themselves... Great question. ..it would have been in water, presumably. Did that person punch the water? Well, but just what would they have done? And also, my other question was, were we happier before we saw ourselves? There's a lot there to unravel. I mean, it's interesting because one of the tests of self-consciousness is not kind of reacting angrily at your reflection.

11:18So probably by the time we'd reached that stage, that we were able to, you know... There may well have been another creature, you know, as we go up the tree of life. But that's kind of almost part of the definition of being human, isn't it? But when you catch your reflection as an older person, that can make you quite angry.

11:37Russell Foster:We don't have mirrors in the house and if you go to a hotel and you think, ooh, who's in my room? And there's that rather strange large person that I don't know. I think one of the things that happens when you look in the mirror is there's a kind of CGI effect that your brain, or your mind rather puts together a rough version of what you've looked like looking in the mirror for ages and then you see a photo and go, I'm grey and I'm bald not you Brian obviously. Which bit of the scripts is this oh no no i think it's my fault sorry i think the theme is long gone this is not about light at all this is uh about existential anxiety with the nature of aging ryan so what is the origin of light so before artificial light it's the stars yeah that's the origin of light in the universe can you talk us through how it is produced yes so what i was taught at school is it's a bit like an iron bar.

12:30Russell Foster:So you stick it in a furnace and the electrons in the atom go from an inner orbital to an outer orbital and then they fall back down again and lose the energy they've taken up and that is emitted as a red photon of light. And that's the kind of thing I thought the sun was made of. And then you realise in the centre of the sun because of the intense pressure and heat there are no atoms. It's all subatomic particles. And so what you've got is hydrogen nuclei fusing to become helium nuclei. And the mass that's left over is then turned into energy. In fact, it releases gamma radiation. And then those gamma photons move through the multiple layers of the sun, taking tens of thousands of years.

13:17Russell Foster:And with each collision, they lose energy. They eventually get to the surface of the sun, and then eight minutes later, they're on Earth. So that's one way of producing photons. But then going back to our iron bar, the outer layers of the sun, atoms can form once again. And so what happens is that those atoms can be heated up by the gamma radiation, for example. The electrons get excited. They go to an outer orbital, fall back, and then emit light. There's two ways in which the sun is producing photons. And I just think that's extraordinary. And then, of course, depending upon the photons that are produced will depend upon all the effects they'll have when they finally get to Earth eight minutes later.

13:57Your field, part of your work is spectroscopy. So what Russell described in the sun, the sun's atmosphere, analyzing the light from the atmosphere allows us to see what the sun is made of. Indeed, helium was first discovered in that light. So could you talk a bit about that spectroscopy and what we use it for? So spectroscopy is really trying to understand structures with light. I mean, we use it an awful lot in the work I do. If you want to understand atoms and molecules, you can't look at them with microscopes. They're much too small to do that. Whereas if you really want to understand the electronic structure of a material, you can shine a light on something and look at the light that it absorbs or look at the light that it reflects or look at the light that it emits and then use the pattern of that light to understand a lot about that structure.

14:39So it's a kind of technique of using light as a scientific tool to understand whatever you're looking at. In the case of stars, I suppose you look for these spectral lines that correspond to light of particular elements, and it's very clean and it occurs at particular wavelengths. And using that, you can tell the elemental composition of stars or distant galaxies and things like that. Raman spectroscopy, which is my favorite type of spectroscopy, is a vibrational spectroscopy. So there you shine light on something and you make all the bonds within that structure start to vibrate. So it's actually inelastic scattering.

15:14The light that comes back has a little bit less energy than the light that you put in. And you look at the shift between the light that you put in and the light that you get out, and you get this really incredible picture of every single chemical bond within your structure. So you can have a kind of transparent liquid and tell entirely the chemical composition of what that is. And the beautiful thing... I can talk about it for an hour. The beautiful thing about it is it's non-destructive. So you can take kind of beautiful artworks or kind of ancient artifacts, and you can use this spectroscopic technique to tell exactly the composition of the pigment, when it was painted, and so it's extraordinarily versatile, and you don't damage what you're trying to study, you just understand a huge amount about it.

15:53How do you react to that, Bridget? Because that was, when I was reading about that this afternoon, that immediately means that I see the world slightly differently and see the content of the world differently and start to think of it in a different way with that beautiful image of light and vibrations and the understanding of the molecules involved. Well, I think it's about, you know, living on this planet and it's all just matter, isn't it? But I mean... Well, light isn't specifically the thing we're talking about, isn't? But talking about it makes it matter.

16:29Russell Foster:Ah, very good. Thank you. Thank you. Russell, in terms of evolutionary history, When do we first see organisms being sensitive to light? Very early on. And why would we need sensitivity to light? And that's because we sit on a planet that revolves once every 24 hours, so it produces a light-dark cycle. And light sensors and biological clocks seem to have evolved together. Detecting the light-dark cycle allows you to compartmentalize your biology so you can do the right thing at the right time. So it's ancient. and we find photoreceptors and clocks in the very, very ancient life forms. So it's not initially for visual, for seeing?

17:16No, I think that's much later.

17:18Russell Foster:Yeah, much later. The Cambrian explosion, where there was this massive radiation of life. Part of that explosion seems to be that it was the evolution of eyes in trilobite-like organisms. And they could then hunt something else. And if you're a potential food item, you want an eye to detect if you're going to be somebody's lunch. And within the space of a relatively small period of time, I think it was only about 10 million years, you've got incredible diversity. And the evolution of eyes seems to have been part of that explosion. It's not long ago, is it, what, 550 million? I mean, all right, in geological science.

17:54But for most of the history of life on Earth, you have the clocks are the important thing.

17:59Russell Foster:Yeah. And photosynthesis, of course. And, in fact, a colleague of mine in Germany has just got some wonderful new data showing that there are clocks in bacteria and they have these wonderful 24-hour growth patterns. So it's very ancient in clocks. And is the mechanism that we use, that everything uses, I'm essentially saying is there a common ancestor somewhere back three and a half billion years where you begin to see this and we all share it? So there's a very versatile molecule based upon vitamin A. And what vitamin A can do is absorb light and undergo a conformation change. It changes its shape.

18:36Russell Foster:And then you've got a whole bunch of different sorts of proteins that surround that vitamin A. So in us, our visual pigments are highly related. You know, their gene structure is remarkably similar. They've formed a lineage. In the invertebrates, again, they're different sorts of proteins. They're different sort of encoded by different sorts of genes. But again, they have at the heart this vitamin A. So what photopicments are doing, both in the vertebrates and the invertebrates and in very ancestral forms of life, is to harness vitamin A and then couple it to a protein which can then translate that light information into a signal.

19:13Russell Foster:And it can do that in a whole variety of different ways. Bridget, I can see you've been filming a question. I hate to say it, but I will. So I've been using Factor 50 for about 20 years. Factor 50? Yes, on my face and everywhere. Yeah. I've figured out I've got a vitamin D. Isn't it vitamin D? Vitamin D, yeah. Well, that's a really good point because you're making the distinction between a sensory photoreceptor, which is using information to build up some sort of information about the world, as distinct from a photochemical reaction, which is the synthesis of vitamin D. The first stage of vitamin D synthesis is going on in the skin.

19:50Russell Foster:But then those molecules travel to the liver and then the kidney to produce the active form of vitamin D. The important thing about vitamin D synthesis is that it requires a relatively short wavelength, which is UVB. So UVA, which is 95 % of ultraviolet light, and then 5 % is UVB. And UVB is the stuff you need for vitamin D synthesis, and that's what is being blocked by your factor 50. and that's why you've got lower levels of vitamin D. I don't think a lot of people know that. I'm really glad I brought it up. The other thing they don't know is that you can't get UVB by sitting next to a window.

20:32Russell Foster:Most window glass filters it out. So, you know, during COVID, when we're all stuck inside, many people became vitamin D deficient. It might be worth, Jess, we've talked about in passing the wavelengths of light, the energy of light and so on. It might be worth just giving an overview of the, Well, I was going to say electromagnetic spectrum. So in your answer, maybe you could say... You're getting all the easy ones, aren't you, Jess? The pithy yes-no questions. You could perhaps explain why I said that accidentally and just give us an overview of all these things. We've talked about gamma rays, we've talked about X-rays.

21:05Just give us an overview of everything. We've talked about visible light, we've talked about UV. Yeah, OK, I'll try. I think kind of late 1700s, early 1800s, people were getting excited about electricity and magnetism and doing experiments with electricity and magnetism. But it was thought that the two were completely distinct phenomena. And then Maxwell came along, James Clark Maxwell, fantastic British scientist, and managed to create this unified theory that combined electricity and magnetism. And actually within that theory, energy, electromagnetic energy was light. These electromagnetic waves were light waves.

21:38And it would be Hertz who'd come along and demonstrate actually that electromagnetic energy was carried in waves in that we had this spectrum of electromagnetic waves that we now call the electromagnetic spectrum that kind of packaged them into these discrete energies or frequencies. So you had kind of long wavelength, low energy systems, things like radio waves and microwaves up through the visible part of the spectrum. So that's kind of going from infrared light and then red light through to blue and ultraviolet light and then into high energy radiation, things like the gamma rays we spoke about before so this was pretty transformative you know that's a step change over a few years of how you understand light and then how we can manipulate it and from things like you know microwaves that now people rely on to to cook food but also you know x-rays and things like that that we went on to understand crystal structures so it's this phenomenal range of incredible manifestations of light that we can use to do really useful things for the world Bridget have you got any questions about microwavable food I'm playing I'm having such fun with this, because I'm really always trying to work out.

22:45When I suddenly hear you go, oh, I've got a question there. And I'm trying to work out, because I thought it was going to be about bacterial clocks before. I didn't think it was going to be about sunscreen. And now I'm very excited to know where we're going to pick up from this. Well, ghosts. I think if people knew more about light, we'd never have believed in ghosts. That's what I think. Why? Because I think most ghosts are light. Light source is weird, light kind of, you know. So whatever that is called, I got it. You were good for the first five seconds. I know what you mean. It's the corner of the eye, isn't it?