In Our Time - The Second Law of Thermodynamics

Episode Date: December 16, 2004

Melvyn Bragg and guests discuss the Second Law of Thermodynamics which can be very simply stated like this: "Energy spontaneously tends to flow from being concentrated in one place to becoming diffused and spread out". It was first formulated – derived from ideas first put forward by Lord Kelvin - to explain how a steam engine worked, it can explain why a cup of tea goes cold if you don't drink it and how a pan of water can be heated to boil an egg.But its application has been found to be rather grander than this. The Second Law is now used to explain the big bang, the expansion of the cosmos and even suggests our inexorable passage through time towards the 'heat death' of the universe. It's been called the most fundamental law in all of science, and CP Snow in his Two Cultures wrote: "Not knowing the Second Law of Thermodynamics is like never having read a work of Shakespeare".What is the Second Law? What are its implications for time and energy in the universe, and does it tend to be refuted by the existence of life and the theory of evolution?With John Gribbin, Visiting Fellow in Astronomy at the University of Sussex; Peter Atkins, Professor of Chemistry at Oxford University; Monica Grady, Head of Petrology and Meteoritics at the Natural History Museum.

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Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash radio four. I hope you enjoy the program. Hello, the second law of thermodynamics can be simply stated thus. Energy spontaneously tends to flow from being concentrated in one place to becoming diffused and spread out. It was first formulated to explain how a steam engine worked.

It can explain why a cup of tea. tea goes cold if you don't drink it, and how a pan of water can be heated to boil an egg. But its application has been found to be rather grander than this. The second law is now used to explain the Big Bang, the expansion of the cosmos, and even suggests our inexorable passage through time towards the heat death of the universe. It's been called the most fundamental law in all of science, and C.P. Snow in his two cultures wrote, not knowing the second law of thermodynamics, is like never having read a work of Shakespeare. So what is the second law?

What are its implications for time and energy in the universe, and does it appear to be refuted by the existence of life and the theory of evolution? With me to discuss the Second Law of Thermodynamics is John Gribbin, visiting fellow in astronomy at the University of Sussex, an author of Deep Simplicity, Peter Atkins, Professor of Chemistry at Oxford University, and author of Galileo's Finger,

and Monica Grady, head of meteorites at the Natural History Museum. John Grimbin, before we are going to detail of the second law. Can you give us an indication of how a law which began concerning steam locomotives came to have such a broad application? Can you give us an overview? But it's because, as you said, it deals with heat. It deals with the flow of heat from one place to another. That's one manifestation of the second law. And of course that was hugely important in the 19th century as Britain in particular industrialised and the rest of the world followed suit. If you could understand how heat works, you could build more efficient

steam engines, putting it very simply, and so your industry would be more efficient. But it goes hand in hand with developing technology. As you learn to develop better technology and better steam engines, then you learn more about the second law as well. So these things always in science sort of go hand in hand in a ratcheting process. And it goes back even a bit further than that to earlier in the 19th century. There was a guy called Count Rumford, who started life as Benjamin Thompson and he was involved in boring cannon to make cannon for warfare and he realised that the process of boring out the cannon generated heat in an inexhaustible fashion which is the important thing before then people had had the idea that heat was a kind of a fluid called caloric which

existed in something and if you heated it by friction you'd rub it all out and it'd all be used up and he discovered that no matter how long you kept brining away at the lumps of iron to make cannon you kept producing heat. So there's this realisation that heat was a form of energy. It became understood as a form of energy. And energy, of course, is what drives the whole universe and keeps us going. So it's absolutely fundamental.

Can you tell us just because the listeners will be clamouring to hear this? What's the first law for me, Don't know? The first law is very simple. It's a kind of sort of throat clearing which says that the total amount of energy in the universe always stays the same. And it's been paraphrased as saying, you can't get something for nothing.

and the second law in a similar vein has been paraphrased as saying things wear out and so you're always losing useful energy and what matters is that although the total amount of energy in the universe stays the same you can only do work as in a steam engine by moving energy from a hot place to a cold place and as you do so some heat gets lost in the process

that's the second law at work and eventually as this goes on and on and on the whole universe will end up at the same temperature and if everything's the same temperature you can't do anything useful you can't run a steam engine in which both bits of the steam engine are at the same temperature and so this is the idea that things will eventually wear out entirely

and that ties in with what you're talking about, the arrow of time. There's a past when things are lively and interesting and heat flows from one place to another and a future where everything's cold and dark and worn out. Throughout this first part of the programme we're going to use the steam engine as a metaphor for big bangs for all sorts of change

which will come on to. Peter Adkins, can you introduce us, can we go further into the steam engine and tell us how the theory grew out of the practice because that's one of the fascinating things that these men are working away making this thing to go along railway lines and the theory develops alongside or around it and can you tell us how I say the French physicist

Sadi Kano, what he did about it? Yeah, I think there are really four people who constructed the second law. One is Sadi Kano. In other words William Thompson, Lord Kelvin later and then there was Rudolf Clausius, and finally there was Ludwig Boltzmann, and each made a very special contribution to understanding. Karno looked at a steam engine and tried to identify what was the limits of its efficiency.

Everyone thought at the time that England was producing its munitions. It was pumping its wells and so on, pumping its mines with steam, and the French were terrified, so there was a huge interest in France on making their machines more efficient. And Karno looked at the structure of a steam engine and tried to think what it was that determined its ultimate efficiency. Most people at the time thought that it might be changing the pressure, it might be changing the working substance from, say, steam to air and so on. But Kano came up with what turned out to be an abhorre. absurd idea in the views of his contemporaries, that it was only the temperature, that, as John just mentioned,

a steam engine really consists of three bits. There's the hot reservoir. There's the cold sink where you throw away some heat. And there's the gubbins in between, really, the piston, which converts heat into work. And Karno, by thinking about it in the machine, decided that it was only the temperature of the hot source and the temperature of the cold sink that determined its ultimate efficiency. What were the briefly the chief modifications or extensions at the other three that you mentioned gave to it?

Well, Carnot's views were seen to be so absurd that they were ignored, which I suppose for England was a good thing. But then his book survived in print, and Kelvin came across it and started to think about it in more detail. And he came up with a view that really the most important part of a steam engine was not the hot bit. It was not the piston.

It was the cold bit. And he said effectively, and this is yet another statement of the Second Law of Thermodynamics, that steam engines don't work unless you've got the cold sink. The next person to come along was Rudolf Klausius. And he said something that we all know anyway, that heat doesn't flow from a cold object to a hot object. And finally, Ken, briefly, you've got the other one to go. And Boltzman.

Yet another man whose ideas were dismissed us completely absurd. He was, Bultzman, I suppose, was short-sighted physically, but he saw more into the nature of the world than anyone else. And he identified the molecular basis of the second law, why it is that what we have been saying is true in terms of the behaviour of individual atoms and molecules. And that's, which we'll come on to, I think, is a major revelation about why the world works in the way that it does.

Yes. Monica Grady, Kelvin, and Lord Kelvin understood that you have to let some heat escape if other heat was to use to power the turbines. In other words, some heat had to be jettisoned. Now, where does this fit in? I mean, we've got two very powerful introductions from John and from Peter. Where do we go next then to sort of build up the theory alongside this steam engine? We have to look at where the heat's going to and what this system is.

John referred to equilibrium, and you tend to get equilibrium. and you tend to get equilibrium in a closed system and of course in a closed system you won't get this work happening. Can you just tell the listeners what you mean by a closed system? Oh, a system where nothing can escape. Like a sealed box is a closed system. Like a sealed box. A sealed box is a closed system.

You're not putting heat in. You're not allowing any heat to escape. You have a closed system. Now in a system like that, you're not going to be able to do any work because you're not going to get a change. You're not going to allow heat to escape. And so the big thing about the steam engine, as Peter Atkins referred to, is this cold sink.

And there isn't a big sort of heat absorber in a steam engine. The cold sink is the outer universe. And the Victorians tended to look at things because they didn't understand the universe, had got no concept of how enormous the universe was. They looked at things on a much smaller scale. But now we realize that actually when we're looking just at a sense, simple steam engine on a real way in Britain. It's putting heat

out into the atmosphere which is you know travelling throughout around the globe which then has implications within the solar system within the galaxy and so on. So the whole system is the universe and that is where the heat is gradually

dissipating to us. So we must look bigger than just a simple cold system. The word that comes in now, there's one word that is disorder, things go from order to disorder, from the closed system of order one can say to outside the heat is more disorder than

the liquid. The liquid is more disordered than the solid. So order to disorder is the progression. And then the word entropy comes in. So would you just explain why it came in and what it means, what its usefulness is in this discussion? Well, entropy

is a measure of the amount of disorder in a system. And if you've If you think of a solid crystal, that's a very, very ordered system. You have atoms, you have ions perhaps vibrating in a lattice, but it's quite rigid. If you then melt or dissolve that's solid, you have liquid where you have molecules. Atoms are able to move around much more swiftly in a much more disordered way. And then think of converting that into a gas, which would fill a whole room.

Think of an ice cube, going to a puddle of water, going to steam. You have something that would then fill the whole room. You can't then predict where that molecule is, where that molecule is, which molecule is going to hit a wall. The whole thing becomes more disordered as you heat it up. And you can't go back again in a predictable fashion. You can't say I'm going to take that molecule and put it there. And this is where John referred to time.

This is where times arrow comes in as we have this increase in disorder, this increase in entropy in the universe. It seems to be always pointing in one direction. We can't reverse entropy. We can't decrease entropy on this universal scale. So in that explanation, we're always losing energy and we're always moving towards disorder. And we're always moving towards more heat. We're not losing energy We're just sort of changing the form of energy if you like

We're spreading... We're losing useful energy, yes, yes. We're using useful energy, yeah. We're spreading it all out. We're making it more even. We're going from, say, to use a water analogy, we're going from a waterfall where you've got water going from a high point to a low point.

We're going more to an ocean where everything is spread out at the same level. So just to summarise, from this industrial object came these theories, which now underlie notions as to how the whole thing operates. Peter Atkins, talking what's happening to the

universe at large then when these heat? How do we transfer the steam engine, as it were, to the universe at large? We're on with this theory. Well, I mean, the briefest statement of the second law, which I think we ought to focus on, is that things get worse. If you like, energy

has both quantity and quality, and entropy is a measure of the quality of energy. And so as entropy increases, that is, as the world becomes more disorganized, so the quality of energy degrades. But the crucial point is that although energy may disperse, you can tap into that dispersal and use it constructively. So if you think of the engine in a car, the fuel is... is burning and the energy that is released in that way spreads and also the carbon dioxide and water that is produced

when the fuel burns also disperses. But your engine is a way of tapping into that dispersal and you use it to drive pistons and so on and then you can connect those pistons through gears to bricks which you build into a cathedral and so on. So you can use this dispersal constructively, and that's the crucial idea. And you can transform the same idea to, for example, when you eat in the morning, the food that you ingest undergoes metabolism and so on, it breaks down, it releases energy.

Think of it as fuel once again. And instead of having a mechanical train of pistons and gears like in a car, What you've got is a biochemical train of gears and so on, which can be used to, not in this case, to put one brick upon another to build a cathedral, but to put one amino acid next to another to build a protein. And you can be, so in other words, as you eat and disperse energy, so you grow and the processes of life continue. And you can be even more fanciful, if you like,

that if you think of the random electrical currents in your brain becoming organised by the same kind of process in order to you eat and through the biochemical processes that occur and drive the neurophysical processes in your brain, you think. And so an act of creation like writing a piece of poetry giving this talk, an act of gallantry,

and so on, are all ultimately driven by the dispersal of energy. And that is why it is so far reaching. Both those examples, of course, that ultimately depend on energy from the sun. The fuel we've used in the car has come from stored up sunlight in plant remains, and the food is ultimately from stored up sunlight in plants. And what's happening is that we've got a negative entropy happening locally because the sun is making positive entropy in a much larger scale. I want Monica to unravel that a bit, a negative entropy happening locally.

Can you just describe how the sun works in our system and prevents our own planet from being a closed system and therefore stay with our planet and the sun at the moment and therefore has the effects it has on the entropy here? Could you just take that on a bit? Yeah, certainly. If you look at life and this building up of life, you might think, well, that is something that's becoming more complex.

but when we look at a larger system, like the system which incorporates the sun, then we see what's actually happening is the sun is this enormous ball of hydrogen, and the hydrogen is fusing together to become atoms of helium. And as it does that, it gives out heat and light. And that heat and light bathes the earth. It powers our atmosphere, our climate, our weather. It powers the carbon cycle, the water cycle, so it powers the whole of life on Earth.

So let's move a bit further out now, John Grubin, and go to the Big Bang where presumably if disorder is coming from order, then we can look for a point where there was only order, and we inevitably go back to the Big Bang, is that right? No, that's wrong. It's a big puzzle, and it was a big puzzle until quite recently. The Big Bang, the birth of the universe, seems to have been a very disordered state, and we now know this from looking at the famous background radiation,

the microwave background radiation, which gives us a picture of what the universe was like when it was only a few hundred thousand years old, a few hundred thousand years after the Big Bang at about 13 billion years ago. The universe was very smooth and well distributed, and it was a fairly uniform sea of hot gas. Now, what's happened to the heat is that that heat has degraded

and it's cooled down to become the very cool, background radiation. But what's happened to the matter is that it's been turned into stars and galaxies by gravity. And you have actually made a much more structured system out of a disorder system thanks to gravity. And gravity has a remarkable property which wasn't properly appreciated until relatively recently is that it runs this whole process backwards. It can make entropy run backwards and create order where there wasn't order before. Can you introduce, can you develop the idea of Monica Grady of the heat death, the universe following an inevitable cause towards what will be a heat death of the universe because of the working of the second law of thermodynamics?

Yes, this follows on from what Peter was saying about this constant expansion and the constant flow of energy. As coming back to our star, it converts hydrogen to helium, gives out heat, that hydrogen will eventually run out, the helium will be converted to carbon, and giving out more heat. This is happening in all sorts of stars. Some stars explode, become supernovae, again, giving out huge, tremendous amounts of energy. And all those processes within our galaxy,

and in every galaxy, are leading towards a gradual equalization of the energy within that particular system, and then spreading out between the different galaxies. And each galaxy is not in isolation. surrounded by a halo of material that we can't see. It's sort of within a sea of dark matter. So within our whole universe, gradually the stars will build up elements,

explode as supernovae, turn those elements back in to the interstellar medium, start new stars forming. It's a constant cycle. But eventually that cycle will run out of hydrogen, all the hydrogen will have been converted into other elements. It was a hydrogen that was formed in the Big Bang and gradually the whole thing will become dissipated

throughout the whole of the universe and the temperature will gradually have dropped and equalized all over and will go, this is the heat death by that time. Everything is the same temperature all the way through and no work can be done.

In your Peter Atkins, your book Galileo's Finger you use an example of an astronomical clock in Prague to illustrate the illusions you put it of complexity and the reality of growing disorder it's a very good, it's a very clean metaphor to take us on from the steam engine

we go from a steam engine to a clock as we went our way but can you just say why you think that illustration is important and I'll come back to you because you've got a process which is driving a complicated collection of interacting gears if you like

which give rise, I think, as I say there, to the acts of the apostles, as these images move around the clock in Prague. It really summarizes what we've all been saying, that you've got essentially a driving force, which is simply the natural tendency of energy and matter to disperse. In this case, it's the falling of a weight which disperses its energy through friction and so on. So it's irreversible in the sense that the weight falls,

the energy is distributed into the rest of the universe. But there are gears that are driven by this fall. And the gears drive one apostle out through one door, another apostle out through another door, and they do funny little things and so on. And that really captures what we are. That really captures the basis of the biosphere. In our case, as Monica said,

the driving force is the sun. That is the hot source of this solar steam engine that it gives rise to, it dissipates its energy. But the vegetation on Earth, if you like, provides an analogue of the pistons and the gear wheels of a real steam engine and drives the processes of growth on Earth. and then we use the vegetation that the sun has driven to drive ourselves.

So it's a whole sequence of one object using a particular fuel to create more fuel for another object. The business of order to disorder, things become more disorder, seems to be contradicted by evolution. One of the things that happens in evolution, lots of different things happen, but one of the things happen is that life becomes more complex and I suppose our brains are the best example of that, becoming more and more complex.

So how is this second law of thermodynamics, things getting worse, having things becoming wearing out, things more disorder, and we're becoming more... Can I monitor us? Monica, have a go at that first. You're still looking at a very small system there, where you're looking at it.

It's still part of it. Yes, we're part of the system. So if we're looking at something becoming more complex in this particular part of the system over here, that doesn't necessarily mean that it's not echoed by an increase in disorder somewhere else. So again, it's still all being powered by the sun, this

increasing complexity. But how does that sit with the idea of things becoming more disordered, therefore less organized, when a lot of this happening in evolution is we've been more complex and more organised? Now, your explanation is, ah, but disorder is happening in somewhere else, and by this

magic inevitability of ill-eclibrium, the disorder somewhere over there, oh, way way over there with a wave of the hand, is balancing up the increasing complexity in order here. But where is over there? And why is complexity happening here? They're connected.

The interesting things happen, what you're called in complexity, interesting things happen where there's a flow of energy. And so you have to be sitting in the flow of energy in order for interesting things to happen, whether it's a waterfall or a human being. Energy is passing through the system. So that energy has to come from somewhere and it has to be connected to you.

And in our case, it's coming from the sun. So the increase in entropy produced in the sun is creating the energy flow which makes us produce a corresponding but smaller change in the opposite direction. But doesn't it give you any pause that this is contradicting the Second Law of Serminian matter? Things are not getting worse, the things are not wearing out, the things are not becoming more disorder, things are getting more complicated, some people are more than that. We are local abatements of chaos.

We are driven into complexity by the creation of greater disorder elsewhere. But where is this elsewhere, you keep saying, is going to solve it. It's on the sun, ultimately. I mean, it's the dissipation of energy on the sun, which is driving events in the vegetation on Earth. Animals eat the vegetation. They use that as fuel. That drives their processes,

including their growth, their reproduction, and their thinking, and our thinking. It's like, in a sense, the analogy to keep in mind if you sat in front of a screen in which there was a weight on the floor, and you saw the weight go up, you think it was a miracle. But then if you look behind the screen and you see that in fact there's a weight behind the screen

which is actually falling down and pulling the front weight upwards. So it's when you look at the whole thing that you realise that there is a simple explanation, that is energy is dispersing and driving the events which you think are giving rise to complexity. They are in fact giving rise to

disorder and locally to complexity. Well, it's a need explanation. I mean, it's very good. It's probably absolutely right. It just seems something getting away with it going on. Well, you would say that as a local abatement of complexity, wouldn't you? Well, I've never been paid such a forsome compliment

in my life. But if you just consider the solar system, I mean, we are just one planet within the solar system and the complexity seems to be increasing on our planet, but not on other planets as far as we're aware.

There isn't this increasing complexity, the increasing evolution of a series of life forms on other planets as far as we know, as far as we can see. So we are just a very, very small neighbourhood. I can give a much more homely example of this. An ordinary domestic refrigerator. If you've got a domestic refrigerator, it's by a miracle, it's making things colder inside.

It's taking heat from a colder place to a hotter place, and it's throwing the heat out the back and getting warm. so it's not violating thermodynamics if you look at the bigger picture. And if you have a sealed room and you open the door of the fridge inside and leave it running, what happens to the room? It doesn't get colder because the cold's coming out of the fridge. It gets hotter because the waste heat from the refrigerator is warming the room and because no presses is 100% efficient.

So you're generating more heat outside than you are making cold inside. And that's what we're like. We're like the inside of a refrigerator bathed in the outside that surrounds us in the solar system. I think we'll stop there, gentlemen and ladies. Thank you very much. Thanks very much, really, to Monica Grady, John Gribbin and Peter Adkins. Next week we're going to talk about the legend of fast. Thank you for listening. We hope you've enjoyed this Radio 4 podcast. You can find hundreds of other programmes about history, science and philosophy at BBC.com.com.uk forward slash radio 4.