The Infinite Monkey Cage - What Is the Point of Plants?

Episode Date: February 16, 2015

What's the Point of Plants?Brian Cox and Robin Ince are joined on stage by plant biologist Professor Jane Langdale, physicist Professor Jim Al-Khalili and comedian and former horticulture student Ed Byrne to ask, "what's the point of plants?". How would the evolution of life on our planet have differed without plants, and what would our planet look like today? Most crucially that seemingly dull but necessary process of photosynthesis that we all learned about in school, is in fact one of the most important processes in our universe, and as usual it seems, the physicists are trying to take credit for it. Could there be a quantum explanation for how this amazing reaction works, and if so, are plants in fact the perfect quantum computers?

Hello, I'm Robin Ince. And I'm Brian Cox. And welcome to the podcast version of the Infinite Monkey Cage, which contains extra material that wasn't considered good enough for the radio. Enjoy it! Hello, I'm Robin Ince. And I'm Brian Cox. And today we're dealing with biology, which Brian never used to be keen on, but he is now, because apparently it also involves physics, which is great news for Brian, very bad news for me, because I was just about to start understanding biology, then they turned it into physics, which is far too difficult for me.

You just say involves physics. Yeah. So it includes physics. It kind of includes physics. So biology is a wider subset of science and physics is some small little Venn diagram. Is that what you meant? Absolutely. Inside the physics. Absolutely. Is this going to kick off now? Because I think if you want a neutral

person to referee, that should definitely be the person who knows the least about what you're talking. So therefore, I will take that job. Did he just say then, did he just say that biology includes physics? I think if you were spoiling for a fight, you could probably read that into what he said. Today, we're asking what's the point of plants? Are plants just decorative oxygen factories and something to fatten up animals? Or are plants subtle, intricate machines more complex

than post-modernist vegetarian comedians? Does post-synthesis rely on quantum mechanics? Can Venus fly traps be vengeful? Could life on Earth exist without plants? Do bonsai trees have a height complex? How did plants emerge from the oceans? When is a strawberry dead? We're not going through

that one again. To rescue us from the on-air disintegration of Robin Ince and to tell us all about plants, we have a physicist, a plant geneticist and a former horticultural student, and they are. Hello, I'm Jim Al-Khalidi. I'm a professor of theoretical physics at the University of Surrey. And my favourite plant is a Romanescu broccoli because it has a fractal structure, and that's very beautiful. And it tastes nicer than normal broccoli. You did that brilliantly as if you were on Call My Bluff because you had a little pause. You went, because, as if you didn't really know why.

And now I'm not sure whether a fractal structure is true or bluff watch and learn comic time right okay i'm jane langdale i'm professor of plant sciences at the university of oxford and my favorite plant is maize not only because it's the highest yielding grain crop in the world, but because some beautiful experiments were done with it that have shown us some fundamental principles of genetics, which is a bit of a geeky choice, but I'm the scientist here. She definitely knew what she was talking about. That was very convincing.

Bring it on, the night is young. My name's Ed Byrne, and I dropped out of a BSc in horticulture at Staff Cloud University. And my favourite plant is the alpine aster, because as a lazy student, any plant that has an easy-to-remember Latin name is a good plant in

my book and the Latin name of the alpine aster is aster alpinus that's a plant that helps you out this is our panel Jane the first question is, what is a plant? So is there a scientific definition of a plant? I think we can say that a plant is a multicellular organism that is in the lineage most closely related to green algae. I'm surprised it's that complicated a definition, really. What do you want to say?

Something that's alive that's not an animal. No, I was going to say that. It's not an animal. It's not a virus. So it's not a fungus. It's not an animal. Not a virus. Are they alive viruses?

It's not a fungus thing is a bit of a tricky one for me. I always thought that a fungus was a plant. And now I've been told I'm an idiot. They obviously covered that in third year. I dropped out during second. So if you're a vegetarian, you shouldn't eat fungi. That's exactly the thing. These mushroom soup-eating vegetarians are hypocrites.

Yeah. Fungi are more closely related to animals than they are to plants. It's true! I'm not making true so the common we share a common ancestor with a fungus before so the split between plants and us came before fungus and correct so ed why do you fungi fungi what's the correct term, actually? Fungi, isn't it? Fungi. Is it fungi or fungi or fungi? Depends on your preference. Alkali?

It depends on whether you're ordering an Italian pizza or not. It depends, you know, are you a plant or a plant? Ooh! I'm a plant. He's obviously a plant. Plant? Plant? Ooh, right. I'm a plant. He's obviously a plant. Plant?

This has never been more radio-full than this. So we've got it nailed down then. So it's the lineage that's most closely related to the green algae. Correct. So, Ed, back to horticulture. Firstly, I mean, obviously you didn't complete your degree, but why did you choose horticulture? Before you decided to become a very successful stand-up comedian, did you have dreams of horticulture and wealth?

I used to work with my uncle, who was a gardener. He turned out not to be my uncle, he was actually my father's cousin, but it's a long story. Talking about what lineages are most close to what lineages. But he was a gardener and I used to work with him and I thought, you know what, I'll get a degree in this and proved myself wrong two years in. There wasn't really any great thing.

I came from one of those backgrounds where even though I did quite fancy the idea of becoming a performer, there was a notion that you had to get yourself a trade first and then have that to fall back on. So I wasn't going to go to college and study drama i went to college to study uh horticulture instead and i dropped out and it was pointed out to me when i was on a panel show with jonathan ross once where he just said think about it ed if you'd stuck with gardening you might have your own tv show by now jim i'll ask you what this is the thing. We're doing a show predominantly about biology,

about the nature of plants, and I wondered, you know, why? Why do we have you here as a physicist? Ah. I'm sorry, I didn't mean why are you here. I mean, obviously, hopefully there's a good reason. Ever since the 1920s, 1930s, physicists strode out of their labs,

the quantum physicists, hoping arrogantly that they could solve all the mysteries in science. Now, again, we're seeing another return to that arrogance. We quantum physicists feel we have something to say about biology, molecular biology, because it turns out there are certain examples within biology that you can only explain using quantum mechanics. So that's where I come in. But you're not usurping i mean you

make that sound like it's kind of like no i know the thing that is actually this is is this one of those great kind of moments where you know you you see that science coming together where that you know the disciplines which seemed very i mean at what point do we really see that that moving of the two disciplines beginning to overlap well i think it's funny i mean biologists tend to say we we've got on very well without learning any quantum mechanics balls and sticks models of molecules work very well we don't need anything else physicists feel that biology is very difficult very messy complicated and they much rather do their experiments than their sterile labs in a vacuum at zero degrees and so on where

they can control everything um but they are coming together now and it turns out actually it's the chemists who who've been thinking about this and doing this for years now and it turns out actually it's the chemists who who've been thinking about this and doing this for years now and they're the ones that sort of adjudicating so it's physicists chemists and biologists coming together to tackle problems in molecular biology that we didn't think would need any physics or quantum physics to be specific. And it's not just, you know, life is molecular, biology, which is basically organic chemistry, which ultimately has to be underpinned by quantum mechanics because that's the rules that tell us how atoms fit together.

It's not that trivial, quantum mechanics. It's the non-trivial, weirder aspects of quantum mechanics that seem to be important. And there are a number of examples that we discuss in my new book which is on your table in front of you which I'm assuming you're going to get rants so everything you say is going to have a level

of suspense going and then they there's no time for that though but chapter 4 does cover it Jane if we go back to the we talked about the the the definition of a plant so in the history of life on earth so life begins sometime at 3.8 3.9 billion years ago or so when do we see plants emerge well if we if we take the whole of the life on earth as a year then plants move onto land they didn't quite move they kind of got left behind as the water regressed but plants moved onto land december 7th and we showed up at 9 p.m new year's eve so this is for at least 11 12th of life on earth um so so we we have the

the single-celled organisms the the bacteria and then the algae in the oceans yeah so so is it the is it algae that gets left on the land and that then speciate evolved into land plants yeah so so essentially if if if that hadn't happened, if algae hadn't moved onto land and become land plants, we'd still be fish. We wouldn't have got beyond fish, and we'd still be in the sea. And that's just simply that you need a food source for the animals that would then colonise the land to eat.

Yep, and also enough oxygen. But that's quite interesting. So you'd say that if you looked at Earth for at least 90% of the history of life on Earth, then you would have just deserts, essentially, on the land. You would have no green, because we tend to think of the Earth as always being this prehistoric, verdant place.

But that's 90% of it. You've only got life in the oceans, nothing on land. And then you need the plants nothing on land and then you need the plants to come and then the the animals follow yeah so it was about 480 million years ago that plants moved on to land and that's when it all started you were talking about i mean the incredible change once plants do appear i mean in in models when we actually look at uh for instance people looking at uh images of the possibilities of life on other planets and the possibilities of complex life. So will we always currently in the predictions be looking at something akin to what we have here?

The level, the requirement of something that processes in the way that plants process things? I think so. That's what the physicists say, right? That when you're out in outer space and you're looking at all these planets, if you look at Venus, you see CO2 around it in a uniform atmosphere, right? And if you look at Earth, that atmosphere is perturbed. Why am I answering a physics question? And that's the evidence for life on Earth, when that

uniform atmosphere gets disrupted, right? Right. Why are you answering a physics question? Let me take this. So we're talking about photosynthesis there um so photosynthesis modifying the atmosphere making the atmosphere well preparing it i suppose for complex life forms so so could you speak to that a little bit so the reason that photosynthesis is a prerequisite for complex life? Well, photosynthesis splits water and makes oxygen, and there was no oxygen before photosynthesis. And so we depend on oxygen, so therefore we can't function without it.

So the oxygen on Earth only existed in the form of water? No, no, no. There was... When cyanobacteria produced oxygen in the water, dissolved oxygen, but the levels weren't as high and they weren't on land. Well, there's carbon dioxide, isn't there? Yeah.

But free oxygen. Free oxygen. There was no free oxygen in the atmosphere until plants started photosynthesising. I'm sorry, I don't mean to make it sound like I don't believe you. It's an interesting fact that I'm just clarifying it. Well, I know until something started photosynthesising. Yes, cyanobacteria started it.

They started it in the oceans. Did I nearly give algae credit for something cyanobacteria did? That would have been a mistake. You gave plants credit. They are highly litigious, as a light-formed ghost. So when do we see photosynthesis emerge? In cyanobacteria. 2.7 billion years ago, I think.

So that was around for a long time in the single-celled organisms in the ocean. Yeah, absolutely. And then plants, there was actually an endosymbiotic event, so plants effectively sucked up the cyanobacteria. And that is now chloroplasts, essentially. So plants have chloroplasts in every cell. Not in every cell. In most cells, certainly in cells of the leaves, there are chloroplasts that were derived from ancient cyanobacteria.

So by endosynoviosis you mean one cell getting inside another cell? Yeah. How rare or likely do we think that is from our experience on Earth? We think it was a once-only event. You're talking about a very rare event, a single event, without which there would most likely not be complex life on earth because you wouldn't have photosynthetic plants on the land but it could have happened on another planet somewhere else if there's life elsewhere this rare event that allowed for us to evolve here there may have been another rare event

somewhere else that allowed life to evolve complex life to evolve in. There may have been another rare event somewhere else that allowed life to evolve, complex life to evolve in a different direction. So, yeah, we say it's rare, but there might be all sorts of different ways, pathways to complex, multicellular organisms that never happened on Earth. Well, isn't that always the issue with the fact that whenever we do try and have conjecture

about how life may exist in other parts of the universe, that because we only have one template to examine, that therefore means that however hard we imagine, we are always going to be limited with the reality that we've been given so far. Yeah, usually in sci-fi movies we talk about not being carbon-based, but maybe silicon-based life, but that's not very imaginative. There are so many ways where biochemistry could have taken a different route,

utilising other elements to create complex life that we couldn't possibly imagine. There's a star trek, there's some melancholy rock in one of them. Do you remember? For example. Turns out the cave's melancholy, and you don't necessarily think that, but it ruined my visit to Cheddar Gorge. But there is this...

All of those different ways of... Sorry, Brian. Well, there is an argument that oxygen, the chemistry of oxygen, means that it's essentially a very efficient way of getting energy out of other, you know, sugars. Oxidation is a chemical process. And because it's so efficient, it allows for food chains.

And so you can argue that you don't get complex predator-prey relationships in an environment without oxygen. And that's just essentially chemistry. And that'll be the same everywhere in the universe. Yeah. People are going to be so glad you mentioned chemistry. The biggest thing that I get after every gig I do is,

why is Brian always having a go at chemistry? That was the most positive thing you've ever said. Well, essentially, it's chemistry. We're still setting a slightly downbeat manner, but I think it's enough to... It's quite positive, saying that life on Earth depends on chemistry. It does. It's self-evidently true. But if you push him further, he'll go,

but chemistry is essentially physics. Oh! And you don't even have to push him. He'll lean in that direction quite soon. Look, it's like... Up quarks, down quarks and electrons. That's all you need to build a chemist. Or anything else. You also need one of those big green cross signs, though.

Jim, in your book, which, as you said, is available, someone that gets talked about on this show a great deal is Richard Feynman. Now, you use a quote from him, which I think is quite interesting. He says, the substance of a tree is carbon, and where did that come from? That comes from the air. It's carbon dioxide from the air. People look at trees and they think it, the substance of the tree, comes out of the ground. Plants grow out of the ground, but if you ask where does the substance come from, you find out. The trees come out of the air.

The carbon dioxide in the air goes into the tree and it changes, kicking out the oxygen. It's the sunlight that comes down and knocks this oxygen away from the carbon, leaving the carbon in water to make the substance of the tree. Now, he read that and he went, well, that's not right at all. So, first of all, why did you open with that? Just so it's not right. It's not right because the oxygen in photosynthesis comes from the water, not the carbon dioxide. So it's the water being split. Yeah, we didn't open with that to show how stupid fireman was i mean uh it's true that the the uh people assume that you break carbon dioxide up and then take the oxygen from it and and release it and that's why that's what plants do but but the oxygen is taken from water uh and and the

carbon dioxide is used later downstream correct me if i'm wrong here but the photosynthesis is very complicated uh and i did i will own up biochemistry is very complicated um but the carbon from carbon dioxide is is pulled out later on to make sugars but the oxygen is actually by i guess burning water i mean that's what oxidation is it's burning so this is photosynthesis probably the only example where water is actually burnt, because you're pulling oxygen out. It's extremely difficult, isn't it, to split water?

You can do it with a car battery. That's right. Feynman's quote was simply to show that it's a very simple sort of mechanistical process. Ultimately, it's about atoms bumping into each other and ripping molecules apart and getting energy. He was making it, it was a very reductionist picture. Much as I admire Feynman,

and Feynman's one of our great heroes in science, the point of this chapter is that's not the whole story, that something much weirder is going on in that very first step in photosynthesis when when that photon of light hits the leaf and how that energy from sunlight is transferred down to the reaction center so because you've got to turn sunlight into proper into chemical energy that can be used to sort of pull electrons off of atoms and and that bit relies on quantum mechanics or so so we think so the experiment suggests

light comes in it excites an electron in an atom inside chlorophyll molecule and that electron then is sort of sitting above where it likes to sit so it's in an excited state and that's called an exciton and the way that energy is transferred people thought it just sort of bounces around randomly between the chlorophyll molecules and eventually finds its way to where it's needed in the reaction center to be put to use. But it can very easily, that electron at some point will fall back into its original hole and the energy is lost and it's wasted. And yet that step in photosynthesis is remarkably efficient. It's nearly 100%. They realize the way that energy moves through the chlorophyll molecules doesn't bounce around randomly,

but it follows multiple paths simultaneously. So if anyone knows anything about popular accounts of quantum mechanics, the two-slit experiment, the particle, the electron going through both slits at the same time, here this lump of energy is both slits at the same time. Here, this lump of energy is following multiple routes at the same time to find the most efficient way to the reaction centre. So that's where quantum mechanics comes in, something that Feynman couldn't have possibly have known about because we've only discovered it in the last decade or so.

So it's a purely quantum mechanical process. It's not what you call school chemistry. It's still chemistry. It's still chemistry, yeah. And it's not quantum mechanics in the sense that, you know, of course chemistry ultimately must rely on the rules of quantum mechanics. No, it's the non-trivial, weirder aspects of quantum, quantum coherence. And no one thought this could go on inside a living cell because living cells are too hot and messy and complex. quantum effects like this are very delicate and they're very quickly lost i mean after all that's why we have so much trouble trying to build a quantum computer this is what we're trying to do maintain these delicate quantum coherence effects

for as long as possible and people did sort of back of the envelope calculations years ago and decided that inside life forms inside organisms, these quantum effects should disappear in femtoseconds, which is a thousandth of a trillionth of a second. And yet here it is lasting for biological timescales long enough for that energy to find its way to where it needs to. When this was first mooted, this idea of quantum behaviour and photosynthesis, it was, I think know in the physics community as well this was kind of you know what how was it in in your community in terms of this

when this idea was first suggested i think it was broadly accepted i mean i think it's it's right it is it it is physics underlying it that certainly the light reactions um of course you know we've how many years have we spent trying to persuade school kids that plants are interesting even though they have to learn photosynthesis and now we've got to persuade them that it's interesting and they've got to learn photosynthesis and quantum mechanics i mean yeah this is not necessarily a good thing for the field but when it was explained to me a lot of that was left out i have to admit are you relieved you didn't do horticulture now ed because this is i was like when reading some of the things before the show

where to have grass, for instance, described as a quantum computer, that suddenly, you know, changes the view of a garden in quite... It's quite a narcissistic quantum computer because it only has the one particular measurement it does, but still, these... Grass is a narcissistic quantum computer. Well, it's not like... What else are you going to find out right grass what

does that mean what other questions are you going to throw into that quantum computer you've just found out it's just grass it just remains grass it's all got all that intelligence so smart you do all that quantum behavior what does it do it just remains growing ridiculous it should use its quantum computing abilities for other things like what what? Well, I don't know. Finding out the kind of questions Jim's got in physics. Some really hard stuff there. Grass. You think your lawn should do physics? Yeah, I do.

And because it doesn't, it's a narcissist. Well, I just think it's lazy. It's lazy. It doesn't flower or anything, does it? It just grows upwards. When it gets tall and long, when it gets caught in things. And it hides dog excrement very easily. It does flower.

It flowers. It flowers. Yeah, but not in a proper flowery way, does it? If I went home to my wife and I went, look, I've got you a bunch of grass, that's going to suggest the beginning of a divorce. I'm not now going to say, well, someone, a scientist, told me, actually, it is a flower. Stop whining.

Do you think that all grasses are long? There's lots of different grasses. There are a lot of different... I was thinking a particular kind of grass. Stop whining. Do you think that all grasses are long? Have you seen those seeds? There are a lot of different... I was thinking of a particular kind of grass. You're generalising about grass in a very unfair way. I will challenge you to find a grass that your wife will go, no, that really is what we wanted in the vase

in the middle of this room. What a centrepiece. I'll find you one. He's going to say, there is one. There is a type of grass that keeps my wife very happy. I think it's only nicknamed grass, though. I think we really got technical about it. But I enjoyed my time studying horticulture when I did it.

And the relationship we have with plants and the relationship that plants and animals have with each other in agriculture, for instance, is very interesting. The fact that, like, talking of grass, we can't eat grass, but cows can, and we can eat cows. And then a cow

does a poo, and we can't eat that poo, but we can feed that poo to turnips, and then we can eat the turnips. See, animals and plants have been in league with each other to make themselves indispensable to the agricultural process for a long time they're in league is what i'm saying but because we do we we feed animal products to plants which i always enjoyed telling vegans when I was at university.

Because sometimes you... I have nothing against vegetarians. I love my best friends. Sometimes you have people who are overly political vegetarians and vegans and they literally scowl at you for eating jelly babies. I swear to you somebody gave out to me for eating jelly babies like I was just tucking into a packet of crunchy cow kneecaps. Because there's gelatin in them. And somebody gave me that and I said,

well, your organically grown salad is grown using the surplus from slaughterhouses. Because we feed salads and we feed vegetables, organically grown vegetables, we feed them dry blood and pumped up bone. And when you tell that to a vegan, they turn green. But they still can't photosynthesize it's interesting jane though because robin's um prejudice against grass against it but i just want it to do more sometimes but it reveals that don't cut it

and it will i don't and then i'm told off for that as well and i cut it and i bring it home and put it in that vase but that reveals that there is an idea that you just plants you know we will listen to the title of this the monkey cage you say well plant you know they're complicated uh organisms extremely complex aren't they they are and they've had to evolve um quite intricate ways of being more plastic than we are, for example. So, you know, if we get hit and knocked over and our arm gets taken off, it won't get put back on. But if you take a branch off a tree or a plant, it'll just grow it again. It's plastic. It takes whatever the environment throws at it.

It can't run away. And it just rechanges its growth program depending what's plastic. It takes whatever the environment throws at it. It can't run away, and it just rechanges its growth programme depending on what's happening. So if the light's coming from one side, it grows towards it. If the light's coming from above, it grows up. If it senses gravity, if it's upside down, it will turn around and go the other way. Actually, what's very interesting about plants

and that whole thing of, like, phototropism... Yeah. ..is that it turns... I went out for a day with a guy called Tristan Gooley who's known as the natural navigator. He's a very interesting bloke. Maybe you should have him on. And what phototropism does,

because in, say, in Britain, for instance, the sun is always just to the south, plants in general grow towards the south and it turns every tree virtually into a compass. If you ever can't find your way you can see it's more thick lush growth on uh on one side it's quite handy you did learn something see so i saw a film in 1975 called the mutations in which donald pleasance plays a mad scientist who kidnaps people with the aid of Tom Baker and then splices them together with plants in the hope that

eventually they'll photosynthesise to be a solution to world hunger problems. Jane, how possible is that? I'll tell you that it's probably not possible because there are sea slugs. I didn't even tell you this. This isn't even scripted, is it? There are sea slugs that

have... I love the idea that the rest of it is. I wish I'd been sent a copy of this script. There are sea slugs that eat brown algae and they absorb the chloroplasts. And if you starve the slugs, they will photosynthesise using those chloroplasts. But there are two different species.

And if you starve them both, if you basically stop feeding them, they will photosynthesize using those chloroplasts. But there are two different species, and if you starve them both, if you basically stop feeding them, they will photosynthesize. But one species dies after 10 days, and one dies after 30 days. And it's not because the chloroplasts are doing anything differently. It's because the slugs can't cope with the reactive oxygen species that are being produced by the chloroplasts as they try to photosynthesize. So basically what plants have done is evolved very intricate mechanisms of detoxifying those highly energetic oxygen species and i doubt i doubt if you spliced your whatever it was you just said onto a plant they would be

able to do to detoxify them to be honest i remember watching that film we're thinking i'm not sure they did employ a science advisor it was yeah it was it was worse than sunshine anyway jim it sounds uh as if you said that the the quantum mechanics that appears to be operating in photosynthesis is unusual you said that this this quantum you call it the decoherence but this quantum state seems to be existing for a very long time. So is that going to teach us, studying that system, is that going to teach us as much about quantum mechanics perhaps as the quantum mechanics teaches about biology? It could do, yes. MIT physicists who are trying to build a quantum computer first read this paper about plants actually, you know, grass being a quantum computer and carrying out this quantum weirdness.

And they thought it was ridiculous. You know, here we are trying so hard to maintain these delicate quantum effects, and life seems to have hit upon this trick. It may be that we can make use of it. We don't know. I mean, I could imagine, for example, learning from nature, the way it transfers that sunlight so efficiently down to the reaction centre, maybe in developing better, more efficient solar cells. You know, it's something that we struggle with.

The way we make use of sunlight to convert it into electricity is very inefficient. If we could find a better way of doing it, that would solve our energy needs. So if nature's hit upon this first, then maybe we can learn a lesson from it. But it's too early to say. to say, but it's possible that we can follow from the tricks that life has evolved over billions of years to

learn how to utilise quantum mechanics and why not? If there's an advantage to be had, then life would have found a way of doing it. So Jim, we have a final question for you, which is when you were in your early days as a physicist, again, this move into quantum biology, would you have imagined that this was the you know the kind of

book you would be writing this you know and and how excited are you about these two disciplines coming together well uh i have to say of course i co-wrote this book with a molecular biologist john joe mcfadden uh i wouldn't have been able to write the book by myself i don't know enough biology and biochemistry to do it. John Joe works in the same university as me at Surrey, and when we started talking about quantum effects in biology, a lot of people both in my department and his told us, look, this is barge pole time. If you want to maintain your credibility,

I think someone said academic credibility is like your virginity. You can only lose it once. And, you know, venturing into a field where... Venturing into a field which is controversial, which is still not part of the mainstream, is to some extent a little dangerous. My day job in physics is theoretical nuclear physics, which is equally exciting.

But I'm using the tools that I've... You know, the quantum mechanics that I apply inside the atomic nucleus now in some of these examples in biology. So it is surprising. I think, you know, five, ten years ago, it would have been... I wouldn't have taken the plunge and written this book or got involved in research in this area. But I think the time is about right now.

We're sort of on the cusp. Five years ago, it was too soon. Another five years from now, every Tom, Dick and Harrowby will be doing quantum biology. So it's nice to be at the forefront when not too many people are sort of elbowing you out of the way. And even if you do lose your academic credibility, you've made it sound really racy, haven't you?

Have you lost your academic credibility? Oh, not yet. I went into a forest with a biologist, but it never worked out. So, thank you very much. So we've got somewhere we have, as usual, we've asked the hive mind of our audience

for their opinion on plants. And we asked you, if you had to remove one plant from the face of the earth, what plant would it be and why? Roses, the answer is. They are a shocking cliche and no other flower has a chance on special occasions. Class. Robert Plant,

why did you leave Led Zeppelin? Echinacea, to annoy homeopaths. Wouldn't it annoy homeopaths? Because if it didn't exist anymore, the increase in the nostalgia makes it more potent. So, we finally... Thank you very much.

If you say thank you to our fantastic guests, who are Professor Jim Al-Khalili, Professor Jane Landau, and, of course, Archdeacon Ed Byrne. And then we just have emails. We've had a lot of emails. Here's one. I'm a huge fan of the show. Keep it up.

I have one grievance with your show, which is the title of your programme. I can visualise a cage with one monkey inside it, but along comes another. Easy fix. Make the cage twice the size. However, if an infinite number of monkeys came along, you could increase the cage to infinite size,

but as there would be no boundaries, there would be no outer cage and no space inside the cage to keep the monkeys in. Yours disappointedly, Ben. That makes no sense. I think the disappointedly is probably Ben's parents, really, when you think about it. What's he doing now? Oh, he's upstairs writing another letter to the radio. Here's another one.

If there are an infinite number of universes, is there one in which there can't be an infinite number of universes, and could that be this one? The next bit is the bit I like. A simple answer will suffice. No is the answer. Because if there's a multiverse, then it exists according to some laws of nature, and those laws of nature will apply to all the universes in the multiverse.

True, but the idea of a multiverse is... In terms of solving the problems of quantum mechanics, it's very cheap on assumptions but expensive on universes. I prefer the Bohmian mechanics interpretation where there's an objective reality rather than being a logical positivist like you.

Ah, but there you're talking there about the quantum multiverse of many worlds and the manifestation of quantum mechanics. I'm talking about cosmological. Anyway, that's all we've got time for today. So thank you very much for listening.

Thanks very much and goodbye. Thank you. So thank you very much for listening. Thanks very much and goodbye. Goodbye. Feeling that nice again? game. This is the first radio ad you can smell. The new Cinnabon pull apart only at Wendy's. It's ooey gooey and just five bucks with a small coffee all day long. Taxes extra at participating Wendy's until May 5th. Terms and conditions apply.