The Infinite Monkey Cage - Illuminating Light - Jess Wade, Russell Foster and Bridget Christie

Episode Date: August 20, 2025

What is light? How has it shaped our understanding of the universe, our biology, and even our culture? In this illuminating episode Brian Cox and Robin Ince shine a spotlight on the fascinating science and history of light. From sun and circadian rhythms to the dazzling complexity of quantum, they explore how humans have understood and been influenced by light across time. Joining them to shed light on the subject are physicist Dr Jess Wade, Neuroscientist Professor Russell Foster and comedian Bridget Christie. Together, they trace the story of light from early scientific theories to the cutting-edge research of today. Expect tales of light emitting eyes, the mystery of wave-particle duality and why Bridget thinks that if we had understood light better, we’d never have believed in ghosts!Series Producer: Melanie Brown Assistant Producer: Olivia Jani Executive Producer: Alexandra FeachemBBC Studios Audio Production

BBC Sounds, Music, Radio, Podcasts. Hello, I'm Brian Cox. I'm Robin Nitz, 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 a 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 and what is light anyway? To help us understand light we are joined by a circadian neuroscientist a Raman spectroscopist and an existential biker and they are.

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. Hi, 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. So there are these particular types of beetles called dual 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. So 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. Well, I'm Bridget Christ. 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. Can I just ask, when you were talking there about the left hand or the right hand of the spiral there, because I'd never realized Ursula Le Guin's book, Left Hand of Darkness. So could you just explain the left hand and the right hand thing? What 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 carality 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 the kind of fancy way of saying they have a handedness. So your hands, if you put them together palm-to-pal and 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 GCSEs did you do? Probably the same ones as you? I didn't do any. Okay. 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 behaviours. But historically speaking, when do we start to think of light 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 it was, even Leonardo da Vinci thought,

about that for a while. And it was so our understanding that it's light reflected off of objects into the eye that allows us to see is a relatively late phenomenon. I never understood that. Because as you said, Bridgett, when you go into your room

and turn the light on, how did Leonardo da Vinci not figure out that the light is not coming out? I suppose it was one of these seconds. Why did you not invent the light? It seems obvious that you can go into a dark room

and you can't see anything. am I missing something? 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? Yes. Where it's almost like everything. I'm afraid it's time for clothes 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 and they thought he was going to die. And the qualmast goes, some of you've nearly died as well, haven't you? Bob, you've nearly died.

He goes, yeah, I did nearly die. I didn't like you. Michelle, you've nearly died, haven't you? Yes, I did. And he goes, Daisy, you did die, didn't you? And 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 is the most beautiful thing. But I wonder, yeah, that's an interest, that, you know, why that sense of the shrinking? 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 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 as you described it. Yeah, about early 1,000s. 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, Ibina al-Haitan, who really defined this kind of optical geometry and actually built the first camera obscure

to be able to be able to look at it. So had predictions and understandings about reflection and refraction and how light interacts with surfaces or passes through different materials. And then until about 1,500, people started playing around with lenses and optical components and things like that.

And then through that 1,400s, 1,500, 1, 1,600s, people had become obsessed with trying to define what light was. So you had these competing theories. You had Newton, who was 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, you 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 experiments

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. So this was a massive thing.

It was in London. He showed it at the Royal Institution. So that was 1800s. Everyone was then convinced, okay, lights 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, 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. Yes. See, that's a beautiful. I was just, I don't know if you've seen it.

There's a cat on Instagram. 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 it would have been in water presumably did that person punch the water 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. So probably by the time we'd reach 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. Yeah, well, we don't have mirrors in the house. And if you go and you go to a hotel and you've, oh, who's in my room? and there's a rather strange large person than 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? I think it's my thought, sorry. I think the theme is long gone this is not about light at all. This is about existential anxiety with the nature of ageing.

Russell. So what is the origin of light? So before artificial light, it's the stars. 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. 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 realize in the center 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, 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. Your 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. It did 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. So 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 favourite 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 and so it's actually inelastic scattering the 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 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 artefacts and you can use this spectroscopic technique to tell exactly the composition of the pigment when it was painted.

So it's extraordinarily versatile and you don't damage what you're trying to study. You just understand a huge amount about it. How 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, specifically the thing we're talking about isn't. But talking about it makes it matter. Oh, 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 seeing. I think that's much later. 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, if you're a, if you're a, if you're a, 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 be part of that explosion. It's not long ago. Is it worth 550 million? I mean, all right. In geological science. But for most of the history of life on Earth, you have the clocks are the important thing. 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 growth patterns. So it's very ancient. And is that, is the mechanism that we use that everything used? Is it, I'm essentially saying is there a common ancestor somewhere back four and a half billion years where you begin to see this? Yeah. And then 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 confirmation change. It changes its shape. 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. Their gene structure is remarkably similar. They've formed a lineage.

In the invertebrates, again, they're different sorts of proteins. They're encoded by different sorts of genes. But again, they have at the heart this vitamin A. So what photopigments 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 and it can do that in a whole variety of different ways. Bridget, I can see you've been forming 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 figured out I've got a vitamin... Isn't it vitamin D? Different D, yes. So A... 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, 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. 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 lights and so on Might be worth just giving an overview of the Well, I was going to say, electro-magnetic spectrum So in your answer, maybe you could say Why? You're getting all the easy ones, don't you, Jess?

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. We've talked about UV, we've talked about UV, so... Yeah, okay, 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. And it would be Hertz who'd come along and demonstrate actually that electromagnetic energy was carried in waves and that we had this spectrum of electromagnetic waves that we now called 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 red, 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 cook food, but also, you know, x-rays and things like that, we went on to understand crystal structures. So it's this phenomenal range of incredible manifestations of lights that we can use to do really useful things for the world.

Bridget, have you got any questions about microwavable food? I'm having such fun with this, because I'm really always trying to work out. When 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 sources, weird, light kind of, you know, that, whatever that is called on it.

You were good for the first five seconds. I know what you mean? It's the corner of the eye, isn't it? And we get a little bit, so we only see a slight bit. But then a kind pattern-seeking brain puts together a flamboyant image of a beheaded, you know, 17th century explorer. There was one.

uncanny the very good podcast actually but there was some instance of someone seeing figures in the living room and then turning a light off or going back in and seeing them there and then they weren't there and I said yeah but when you turn a light off and you close your eyes or open them you can still see that image there and that's all I've got to say about that actually why is that so if you see a bright light for example if you should stupidly look into the sun you'll see that sort of image of the sun for some time afterwards, and that's because you've essentially overexcited your photoreceptors, and they're

still firing and sending signals into the brain. So it's not your brain that's kind of remembering it, it's the actual chemical level, yes. But I think, you know, if we're going to go back to ghosts... No, we're not. I think everyone wants us too. Then it's

perfectly possible for the brain to form an image. But going back to Jess's point about the electromagnetic spectrum, I thought it was fantastic. how ultraviolet light was discovered. I forget the chap's name. But the discoverer of red, infrared light had been made. And he thought, well, I wonder if there's something

at the other end of the spectrum. So he got a prism, and he put photographic paper beyond the violet end of the spectrum, and it went black. And it went black really quickly because, of course, the ultraviolet had a lot of energy. It's not that long ago, is it. I mean, x-rays is what did you say in the 20th century,

1897 or so, isn't it? And kind of remarkable things have come from the discovery of x-rays and then the manipulation of x-rays. I mean, I think it's still the only father-son pair, the brags, to win the Nobel Prize for using x-rays to decipher crystal structures. So understanding the crystal structures of so many of the complex biomolecules and proteins through the DNA, that all came from being able to, well, A, understand x-rays and then be able to use them to investigate different atoms and materials. That is an interesting story. so perhaps you could talk a bit about the discovery of the structure of DNA because it goes to the heart of what you mentioned. If you think about it for a moment

and you don't know how it was done, it's a remarkable thing that you can discern this double helix structure. Do you want to take it? I think you're more of an expert in this scenario. Bridgett, would you like to? Yes, I'd love to. X-rays are really interesting for lots of reasons, but one is that the wavelength of x-rays

loosely corresponds to the spacing of atoms within a crystal, and that makes them a really interesting tool to try and understand the structure of a crystal so when you crystallize a material all of the atoms arrange in rows and columns and things like that such that if you bombard them with x-rays the x-rays because they have that wavelength that corresponds to the spacing between those atoms

kind of scatter and defract and generate all of these cool and interesting patterns where if you study the patterns that those x-rays have made after travelling through or bouncing off this crystal you can work out what the arrangement of those atoms were inside that crystal. So there was a beginning of the 1900s

this real increase in the use of x-rays to decipher all of these different complex molecules that we knew existed, but we didn't know quite how the atoms were arranged inside those molecules. And there was a particular generation of women scientists who were taught in a certain way at school,

which meant that they were really well-tuned to kind of pattern recognition. And there was this kind of boom of Dorothy Hodgkin, of Kathleen Nonstale, of Roslyn Franklin, who all came to these crystal structures and had been so well trained to understanding how you could correlate these patterns to whatever was happening in this crystal.

They deciphered extraordinarily complex things like Roslyn Franklin getting the structure of DNA, which was a really massive thing to be able to do. As you mentioned, the double helix is really complex and to be able to see that in these patterns you get of x-rays or Kathleen Nonstale discovered the structure of benzene and went on to be the first woman to be elected fellow of the Royal Society. So they were eventually recognised,

but it was particularly this training they had had in school school that meant when you looked at these patterns of x-rays that bounced off these crystals, you could understand what the structure was inside that crystal. I think that's really remarkable. I think bringing it back to the visible spectrum, I think that's transformative. But if you think about how light, visual light, was bent by a lens in a microscope, for example, and hooks micrographia into what, the 1660s, this was the first visualization of fleas or head lice or other sorts of, you know, and essentially it transformed our understanding of the of the life we share our lives with.

So the way that photons are bent or where they bounce off of objects has genuinely transformed our understanding of the entire universe. And I just love the idea like Hook was just playing around with these microscopes and seeing what you could do with them. Kind of complete master of lots and lots of different things

but was the keeper of cool equipment at the Royal Society? He had some funny title that basically meant he just built cool stuff and then took this instrument to be able to explore all of these remarkable different things. So there's a lot of... of joy that can come from playing with light. Keeper of cool equipment.

I don't know if that was the technical name in the 1600s, but he'd get that title now. What are we learning about what can we done with light to improve health, improve psychology, etc? Yeah, this is a really exciting, I think, relatively new area. The whole concept of why a window is important. It's worth bearing in mind the translation of window. It comes from the ancient Anglo-Saxon, and it means Vinder-Auga, which is for, wind eye because the original windows were essentially holes in the wall that you covered up at night.

So it's a perfect description of what a window was. And now we understand that having a view and being exposed to the world has huge benefits on our health, well-being, reducing levels of depression, making us feel more comfortable and more satisfied. And one of the problems of artificial light is that it's so easy and cheap now to produce that architects are building buildings, without natural light because they can just stick in a bunch of LED somewhere. And so we've been cut off increasingly from natural light.

We've talked about vitamin D, we've talked about views and what a view can provide us. But also there's of course vision, but the regulation of our circadian system, our sleep wake cycles, requires quite a bit of light and for a relatively long duration. And so again, light is

very important in that domain as well. Something I was going to kind of add to that is actually, we go lots to, as scientists to do experiments in something called a synchotron, which is a really powerful source of x-rays. There's one out near Oxford. It's shaped like a big donut. It's a big circular building where they accelerate electrons and electrons moving really quickly, emit x-rays. We use those x-rays to do science.

It's actually where they discovered the structure of the coronavirus. But there, when you get time on this instrument, it's a competitive thing. You have to apply. You say, I've got this fantastic idea for an experiment. They say, come for 72 hours. and you go for 72 hours and you're in this kind of cabin inside this synchadron and you've got to stay up for 72 hours to do these experiments and you sleep on shifts and a lot of people play a lot of chess

and it's quite a weird. You get very close with your lab group during that time but your sleep cycle goes completely off because you're surrounded by the most strange artificial light playing around with the brightest light in the UK ever. You know this billion times brighter than the sun beam of x-rays that you're using to investigate the atoms and molecules that you're working with. So I always find that quite strange phenomenon.

How we create something that wants to emit light is to work out exactly what wavelength range we want to emit, so what energy of light we want to emit. Part of what I think we find so difficult about lots of the new LEDs is how blue they are. That's a particular part of the spectrum that keeps you more alert and focused. We can actually make lots of molecules that are really good at emitting light. So lots of organic systems, organic semiconductors, we call them.

a really brilliant emitting light. They're the O and OLED. If you've got a Samsung Galaxy or an Apple iPhone, they have this Oled display. And that's using organic, so a carbon-based semiconductor, where actually you can really precisely tune the chemical structure of that semiconductor to emit a particular colour of light.

But in your case of wanting to create some artificial light, you'd really need to understand what wavelengths you wanted to get. And then you could go and do some clever kind of computational chemistry to predict what structure you'd need to emit light of that wavelength, and then you'd work with physicists and engineers to make it possible. But a good example of tuning light for a specific task would be in the new plant factories that people are designing, which is, you know, if we ever get to Mars, this is how we will survive,

because these LEDs are tuned specifically to excite photosynthesis. So I think to answer your question, it depends on the nature of the light detecting task. And understanding that is another really interesting spectroscopy challenge. And so if you want to understand, and for these kind of plant houses, vertical farming type systems, you do a technique called hyperspectral imaging. So that's hyper spectroscopy. You'll be pleased to know.

Where you get kind of images of spectra. So instead of just collecting one spectrum, so one graph expressing how light is absorbed or reflected or emitted as a function of energy, you create an image of that data. So you get this kind of hyperspectral cube, if you will, of data where every single pixel in that is its own spectrum. So building on this.

kind of complex array of data, you can really optimize the lighting you use in these kind of indoor agriculture systems. So how did Matt Damon grow his potatoes? I think he had a special imaging system. I think so, yeah. Is that what he had? Undoubtedly, yeah. I have a couple of questions, if that's okay. Please. So fungus and mycelial networks that grow in the dark, the fungus evolves at quite an incredible rate, doesn't it? It's brilliantly adaptive. But in the dark? Well, there will be a certain level of light penetration into the soil, but yeah, it's largely in the dark. What do you think about that? Well, so an analogy would be the blind mole rat, which looks like a grey, hairy sock. On one end has massive teeth, and like a mole, which

burrows using its forelims, this creature that burrows under the deserts of Israel actually bites its way through. It's an extraordinary creature. But it has no superficial eyes. It lives in the dark, but it has tiny little eyes underneath the skin. And what seems to happen is we showed that those little eyes are actually used to regulate the clock. No visual capability whatsoever. But it surfaces from time to time and then sets its internal clock to the external world. So it's sampling light occasionally.

So does mycelium have a clock? Yeah, it will. They certainly have some of the first work on showing that there was a, circadian clock was done in fungi. Yeah. Oh, so they seem utterly fundamental. What is the explanation for why living things, all living things

it appears on the earth, as far as I can tell, require clocks? So if you think about what our biology needs to do, it needs to deliver the right stuff, at the right concentration, to the right tissues and organs, at the right time of day, to provide an adaptive response to this

dynamic world, which is revolving once every 24 hours. You've got to do the right thing at the right time. If you don't, then our biology collapses. And then that's been shown in organisms where the clock has been knocked out genetically, they fail miserably. And so it's essentially fundamental to life. And in fact, when they were looking for life on Mars, then they're actually looking for the formation of organic molecules, according to the Martian Day, which is 24 hours and 36 minutes. So it's regarded as a fundamental feature of life and on other planets. That's what's being looked for.

Are there 24-hour rhythms, or whatever the revolution of the planet is, are there rhythms that correspond to the rotation of the planet? But also in the Mars mission, so the Mars mission has a little Raman spectrometer on board, one of the latest Mars missions, to try and look for signatures of these organic molecules. And so that's using spectroscopy to try and hunt out for these different approaches. There's an interesting story about the Mars rovers,

which of course are solar powered so they depend upon light on the Martian Day and that's not synchronised with the Earth Day and so the poor people running this thing back in Houston were getting completely jet lagged and making mistakes

and so they actually had to turn the rovers off so that the technicians can get some sleep so that they can then effectively operate the rover. It's a good example of a disrupted circadian system and also just a huge feat of science and engineering because actually to do these experiments to perform spectroscopy on Mars, you say it will just build a little compact spectrometer that's rugged and can withstand the journey to Mars

and then being deployed on Mars. But actually the Martian day, the temperature variations go from about minus 60 to 150 Celsius. So you've got to design a spectrometer that can operate and stay stable within that range. So they will have these incredibly cool phase change materials on that basically mean for about four hours you have control of the temperature on this spectrometer. So there's so much thinking that has to go into it. There's no ozone, of course. So they're going to be fried by UVC and even shorter wavelengths. It's incredible. It's amazing. And you mentioned all the wonderful things that we've done in history of science, the things we've used light for. So now, where's the cutting edge? What are the instruments that we're developing now

and what discoveries might they enable? I think one of the really cool, exciting ways that we're using light at the moment is to try and do quantum computing with light. So everyone's excited about quantum globally for kind of computing, sensing, imaging, doing, you know, things we've never thought possible with technologies. An interesting thing about quantum computing is there's lots of different materials, platforms that are still in contention for being the platform that will be chosen for quantum computers. You know, microelectronics, it was all silicon, everyone knew silicon, the semiconductor sector grew from this world of the technologies we have today. Quantum computing could be superconductors, it could be semiconductors, it could be things,

like defects in diamonds, it could be trapped irons, but photons are a really interesting carry of quantum information, and you can encode information in their polarisation or in their phase. We can use existing fibre networks to do kind of quantum communication, and actually they travel really fast and they don't seem to lose their quantum properties. So quantum photonic computing is one of the biggest contenders, and certainly some of the biggest companies that are saying they're getting to a scalable state of quantum computing are using light to do it. So I think quantum computing, quantum imaging, so seeing things with light, speaks a little bit, Bridget, to your point about ghosts. So you can do, just thought I'd say you're a great scientist despite not knowing it, but you can kind of do this kind of quantum imaging with undetected photons.

So you can start to image things using, based on entanglement, you can image things with the photons that don't interact with your system and understand what your system is because the photon pairs you created were entangled by just image things. those photons that haven't interacted and then get these extraordinarily high-resolution images of systems that you've been trying to look at. So quantum imaging and quantum computing, using photons I think is the kind of next huge technological frontier that is so exciting.

Well, we've run out of time. Bridget, well done. Your photon entanglement theory of ghosts was very strong. I don't think that's what was implied or intended. I knew it was what she made. Yeah, I knew as well. So we asked our audience a question,

and we asked them if you could throw light on something in the universe, what would it be? First one I've got is dog poo. Dog poo on the pavement on my nighttime walks. That's a good point. This is the hiding place where all the odd socks go after you put them in the washing machine. They might not be odd socks.

They might be those mole rats you were mentioning. Bridget, where you go? Sorry. a dark place this is wonderful this is pointing out a grammatical flaw

in the question it's one of the most radio four answers it's fantastic because the question is specifically if you could throw light on something in the universe what would it be

the answer is illuminated oh well good well done Why the background smell of the universe is citrus As things can only get bitter Every time, every time

It is remarkable Your D-Reen pun imagination Is one of the strongest things in the universe What have you got? I've got a similar one All the data Facebook has collected As things can only get matter Yeah

This is a, it would be nice to have some sun In an Irish summer Yeah, I've got scary scenes in horror films. Ghosts again. God, that's weird that you sense that person was going to write that as well. I did. Brian hates it when people use their psychic powers on the show because it breaks all the laws of physics.

This is not possible to break the laws of physics. Well, that's what you lot say, don't you? But you would, wouldn't you, for funding purposes. Thank you to our panel. Jess Wade, Russell Foster and Bridget Christie. And that brings us to the end of our 207th episode and the end of the 33rd series of the Infinite Monkey Cage. And it's sad to say, over the previous 6,300 minutes of Monkey Cage,

we've now answered all the scientific questions. So that brings the whole thing to an end. We haven't done all, actually. We haven't done the proton. on entanglement of ghosts, I think, in a full enough way. We haven't done the structure of gas giant planets, and we haven't done anything about, because we were talking about mole rats,

we also haven't done anything about the sense of smell in the vole. In the vol. In the vol. I think the way I pronounced it added something different in the meaning of that sense. There's a lot, a lot of stuff still to discuss then, isn't it? Oh, yeah. So we'll be back. Thanks very much for listening.

Bye-bye. In the infinite monkey days In the infinite monkey cage Done that you're not nice again What happens when at-home DNA tests reveal more than you bargained for? My birth mom was still here, she's still alive? Six new stories of reconnecting and rupturing families. I just couldn't believe it.

I had a sister, after all. Lives upended and long-buried secrets. I then wrote back and said, look, the ripples from this will be enormous. What do you want to do? The new series of The Gift with me, Jenny Clemen, from BBC Radio 4. Listen now on BBC Sounds.