The Science of Everything Podcast - Episode 6: Thermodynamics

Episode Date: November 21, 2010

An introduction to the principles of thermodynamics, including a look at temperature and heat, the laws of thermodynamics, perpetual motion, methods of transferring energy, and the phenomenon of entropy. If you enjoyed the podcast please consider supporting the show by making a paypal donation or becoming a patreon supporter. https://www.patreon.com/jamesfodor https://www.paypal.me/ScienceofEverything

and welcome to the Science of Everything podcast. I'm your host, James Fodor. In this podcast, I discuss a wide variety of topics in both the natural and social sciences, exploring the many fascinating scientific discoveries that can help us better understand the world in which we live. This is the sixth episode, and the topic for today is thermodynamics. So in this episode, I'm going to look at, start off with temperature and heat, and move on to the four laws of thermodynamics, and then we'll have a look at transferring energy, methods of transferring energy from one place to another, and we'll finish up with an analysis of entropy. So, first of all, what is thermodynamics?

Thermodynamics refers to the study of the movement of energy, and also the conversion of energy from one form to another, and also how this affects properties such as temperature, work, pressure, volume, etc. Now, I'm not going to get into the thorny issue of what is energy in this podcast, that's really a whole another podcast to itself. But basically in physics, energy is the ability to do work. And energy comes in various forms, such as kinetic energy, which is the energy associated with motion, gravitational potential energy,

the energy associated with being inside a gravitational field, elastic potential energy, like the energy of a rubber band when you stretch it, etc. Okay, so first we'll start with temperature and heat. What is temperature? Temperature is colloquially a measure of, you know, hot something is, but in physics it has a more specific definition relating to the average kinetic energy of all of the molecules and or atoms, so all the particles, within a particular substance. So that's the average speed with which the molecules within a

substance are moving around and vibrating. Heat refers to the flow of energy between objects due to differences in temperature. To repeat that heat refers to the flow of energy. Heat itself is not a measurement of hotness as such. It colloquially we would say, you know, if you touch a hot stove, you would say, you know, this stove has a lot of heat or something like that. Correctly, we should say the stove has a high temperature. Heat refers to the flow of energy from the stove to our hands, and that's something a little bit different. Heat is somewhat analogous to the concept of work, which refers to the, if you like, flow of energy from one object

to another resulting in an increase in kinetic energy. So if I push a block, I do work on the block, transferring kinetic energy to the block. So that's in a sense the work represents a transfer or a flow of energy. Heat similarly refers to a flow of energy between objects, but that results in an increase in kinetic energy of the particles within that substance and not an actual kinetic energy of the object itself. So heat, energy goes into the particles, they're vibrating and moving around more quickly, Work, the energy goes into the object itself and it moves around more quickly.

So you can sort of see the difference there. Okay, now a further concept in thermodynamics is heat capacity. The heat capacity of an object is the amount of energy required to increase its temperature by 1 degree Celsius. The heat capacity in turn depends upon two factors. The material out of which the object is made and the amount of material present. The more material that is present, the higher the heat capacity of the object. The specific heat capacity refers to the amount of energy required to increase the temperature of a particular substance by 1 degrees Celsius. So that's why the heat capacity of an object depends upon the material out of which it's made.

The higher the specific heat of the material, the higher the heat capacity of the object. So if you like, you've got the specific heat of the material and then the amount of that material, and you multiply those things together, you get the heat capacity. Now, the reason that specific heats of different materials are different from each other is because when heat is transferred from one object to another, or from one material to another, it can be embodied or instantiated in many different forms, and only one of those forms of energy actually increases the object's temperature. So when heat or energy is transferred from one material to another,

it can increase the rotational velocity of the molecules or the vibrational energy, or there are actually many, many different, subtly different ways in which heat can alter the energy of a substance. And it gets really complicated if you go into the details of it. But suffice it to say, only one of those forms, namely the kinetic energy or the translational velocity of the particles in the material, only that form of energy increases temperature. Other forms of energy like rotational velocity, etc., have no effect on the temperature. of an object. So for some materials, so for example if a material has a high specific heat capacity, it means lots of the energy that's going into that

material is being used up in forms like rotational velocity, etc., which do not increase temperature. If the material has a low specific heat, it means that virtually all of the energy that's going into it increases the kinetic energy of the particles and hence increases temperature. So once we know the specific heat of the material out of which the substance is made, and then also once we know how much of that we have, we get the total heat capacity of that object. The high the heat capacity of the object, the more energy we need to increase its temperature by a given amount. Now this concept of heat capacity is important because it tells us a lot about how energy works from flowing from

one object to another. For example, if I take a hot metal object and place it in a bucket of water, the metal object could be hundreds of degrees, whereas the bucket of water could be, you know, 30 degrees Celsius. So the metal object is much, much hotter than the water. But yet, because metal has a lower specific heat than water, and also because, more importantly, there is much less metal than water, you know, you think of a small bit of metal versus a big bucket of water, for these two reasons, the heat capacity of the metal is actually much lower than that of the water.

And so what will happen is that the energy will flow from the hot metal object to the cooler water, but the temperature of the water will only go up by a little bit, because it has a high heat capacity, whereas the temperature of the metal will go down by a lot because it has a low heat capacity. This reason is why we are not harmed by touching objects that are very high temperature, so long as their total heat capacity is fairly low. So for example, that's why people can actually walk on really hot coals. There are various other reasons as well. For example, you have a protective, small protective layer of sweat and water on your feet, which helps to protect you from the from the hotness of the coals. But even more importantly, the coals, although they're very hot,

are also very small, whereas the soles of your feet are relatively large compared to them. Also, coals are not very conductive, so although there's going to be, the energy is going to be flowing from the hot coals, so your relatively cold feet, it's going to be doing so relatively quickly. And because you're walking across the coal, it doesn't have too much of an impact. And so another application of this is why fusion energy is so difficult. Fusion is when you take two, say, small elements like helium and try and combine them together into a heavier element

in order to produce electricity. This is how the sun produces energy. Now some people have sort of intimated that fusion energy would be dangerous. We can't actually do that at the moment. Fusion energy is not yet possible, but if we could do it, some have intimated that it would be dangerous be dangerous because of the massively high temperatures, like hundreds of millions of degrees that would be required, would melt the container and there'd be huge problems like that.

But that's actually not an issue. The reason is because the amount of material that you would have, even if you did have a working fusion reactor, would be so small that even though it was at a ridiculously high temperature, it would have an extremely low heat capacity, just because there's such a small amount of it. So there's actually much more risk and in fact this is one of the reasons why fusion is so difficult to bring about. There's a much greater risk that the container that you're doing the fusion in would cool down the substance and stop the fusion reaction rather than the fusion reaction would in some sense, in some in some in some way melt the container. So the amount of

substance that you have is just as important as the actual temperature of that substance and that's what the concept of heat capacity gets across. When energy is transferred from one object to another, so when you have a flow of heat, often that leads to a change in the state of matter. Now, as you probably know, there are three main states of matter, solid, liquid, and gas, and the states of matter just basically refers to the manner in which the molecules and atoms of the substance are structured in relation to each other. So in solids, the atoms are all very closely bonded together, in a tight relationship,

and liquids, they sort of slip past each other, and gases, they're all dissonable. associated and just move randomly in relation to each other. There are other states of matter as well. For example, Bosi Einstein condensates, plasmas, superfluids, and some other really interesting stuff, but that's an issue for another podcast. As I said, changes in temperature are one of the major ways of changing the state of an object. But an interesting thing that perhaps a lot of people don't realize is that while you are changing the state of a material, say while you are melting it from solid to liquid,

its temperature remains constant. And the reason for that is because, say you're putting an energy, say you're boiling a pot of water, right? You turn on the stove and the flames heat up the water. So they're adding energy to the water. Now, for a while, some of that energy will go into things like rotational velocities and other things I mentioned before, which do not increase the temperature of the water. But some of it will go into increasing the kinetic energy of the water molecules, and hence will increase the temperature of the water. and now that will continue until the temperature reaches about 100 degrees Celsius, which is the boiling point of water. Once it reaches that temperature,

the energy that you're adding to the water no longer goes into increasing the kinetic energy of the water molecules. It will only go into breaking up the water molecules so that they go from being a liquid into a gas. And that breaking up of the liquid molecules involves sort of ripping them apart from each other, which requires energy. And the energy, of course, comes from the heat that you're providing the water.

But the key point is that the temperature of the water does not change during the boiling process because all the energy is going to doing the boiling, and none of it's going into increasing kinetic energy further. So, you know, this has an interesting application for cooking, which tells you that once you've got water to a boiling point, increasing the heat of the stove, is not going to increase the rate at which you're, water is going to cook your vegetables or whatever you're cooking,

all it's going to do is boil the water more quickly. Okay, so that's a bit of a look at temperature and heat. So now let's move on to the laws of thermodynamics, which you may have some familiarity with. There are four laws of thermodynamics, although confusingly it begins with the zeroth law, and then you have the first, second, and third laws. First of all, I'll define this idea of thermolequilibrium,

because it's crucial to understanding the 0th law. By the way, the reason for the 0th law is because the first, second and third laws were elucidated, and then later on, the 0th law was sort of added in as an extra definition to clarify things, so that's why we have a 0th law. Anyway, back to thermo equilibrium. Thermal equilibrium states that if objects of different temperatures are brought into contact, heat is transferred from the hotter object to the cooler object, and this continues until the temperature, which remains.

is the average kinetic energy of the particles in those objects. Of the two objects is equal, at which point the objects are said to be in thermal equilibrium. So thermal equilibrium is when two objects are at the same temperature. When two objects are brought together, heat is always transferred from the hot object to the cooler object until they are at thermal equilibrium. Of course, that applies unless you disrupt the process in some manner.

So onto the zero-th law. The zero-th law states that if object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then objects A and C are also in thermal equilibrium with each other. Now, that doesn't sound particularly interesting. It's just saying basically if A equals B and B equals C, then A equals C. The reason that we need that law is because it's just a definitional thing to define that thermally equilibrium is transitive. So it's not circular in some way that A is greater than B is greater than C, which is greater than A. and that is theoretically possible in some abstract sense. I don't want to get into that too much now,

but the 0th law is just kind of a basic definitional thing to help you understand thermal equilibrium. Now, onto the first law. The first law states that the increase in internal energy of a system is equal to the heat added plus the work done on the system. This is very interesting because it tells us that heat and work are two sides of the same coin. And this is what I alluded to before.

Heat is when you transfer energy to an object that increases the internal kinetic energy of the particles within that object, whereas work is when you transfer energy such that it imparts kinetic energy to the object as a whole. So work and heat are essentially the same thing. It's just sort of the scale on which you are delivering the energy. And this also tells us that mechanical work, which is measured in joules, is directly convertible into thermal energy, which is measured in calories. So, joules, calories, they're pretty much the same thing.

One calories equal to 4.2 joules, but they are both just measures of energy. The second law of thermodynamics is the most interesting and also the most difficult to understand. There are many different ways of stating the second law, but for the purposes of this podcast, I'll just stick with a relatively simple one. The second law of thermodynamics is the one that relates to entropy.

Entropy in an isolated system always increases. Entropy is basically the measure of disorder and I'll talk a bit more about entropy later on so I just want to backtrack and provide another definition of the second law which will be perhaps more relevant to us right now another way of staying the second law is that it is impossible to have a heat engine or refrigerator that is 100% efficient so what does this mean well a refrigerator is an object that transfers heat from a cold region to a hot region now remember normally heat goes from hot to cold

a refrigerator makes it go in the reverse direction cold to hot So if a refrigerator cannot be 100% efficient, it means that it is not possible to transfer heat from a cold to hot region without doing work on the hot region. And remember that when you do work on something, that imparts energy to it. And so increases, in this case, increases the thermal energy of the hot object or the hot region. So for a refrigerator to work, the heat or the energy that is being exhausted to the hot object must be greater than the heat that is being extradited. from the cold object. What about the heat engine? The no 100% heat engine means that if we are using heat to generate work, and an example of that is a power station which burns cold to heat up water, which is then used to turn a turbine, which generates electricity. The increase in the thermal energy of the water is part of the process of generating the electricity.

So we're using thermal energy to generate work. So if we are using heat to generate work, so if we are using heat to generate, work, it is not possible to transform 100% of the heat into work. So some of the heat must be given off as exhaust to a surrounding region. And in fact, that's why all power plants require extensive cooling apparatuses, like nearby lakes or big cooling towers and so on. It's because they have to exhaust heat to their surrounding environment. It's not an engineering problem. It is physically impossible to build a power plant that does not exhaust heat to its environment. Second law of thermodynamics forbids it. If you're using heat to generate work,

you cannot generate 100% of that, transform 100% of that heat into work. And this is crucial for the idea of entropy, so I'll come back to this later when I talk about entropy. The third law states that Absolute Zero may be approached experimentally, but can never be reached. Well, Absolute Zero is the coldest possible temperature.

One Kelvin, you don't say degree, it's just Kelvin, 1 Kelvin is equal to 1 degrees Celsius, but the Kelvin scale just starts at 0, which is equal to about the neg 273 Celsius. So that's the lowest temperature that's possible. And you can think of it this way that if any system has a finite amount of energy, because infinite energy is impossible, then if we remove more and more of that energy, there must be a limit to how much we can remove. And so there must be a limit to the lowest possible temperature that there can be. and that sort of provides the intuition behind the concept of an absolute zero temperature. Now, from the third law, we know that it's never possible to reach absolute zero.

You can get closer and closer to it, so there's no limit to how close you can get to it, but you can't ever actually get to it. So we can say that you can asymptotically approach absolute zero, but never quite get there. So scientists will talk about reaching, you know, two billionths of a degree above absolute zero. or two trillions of a degree above absolute zero and it just gets closer and closer and closer there, so basically it's absolute zero, but they can never quite get there.

And the reason for that is quite complicated and relates to various quantum mechanical effects which are beyond the scope of this podcast, but suffice it to say, you can't ever actually get there. Now, perpetual motion machines, you may have heard a perpetual motion machines, the basic idea of which is that you have a machine which can run forever and produce,

free energy in some way. And there are many, many different ingenious mechanisms as to how this could get to work. And you can look some up on the web and see some of the very interesting contraptions that have been devised. But the specifics of the perpetual motion machine is not really relevant. All perpetual motion machines violate the laws of thermodynamics and so are impossible. Now, if you're saying, I guess there are two different types of perpetual motion machines. One, which is the worst type, says that the machine itself can run forever, and it can produce useful energy output. So it's kind of like the idea that think of a battery that can produce energy and also produce enough energy for you to use and also recharge itself so it always stays charged. They're never as simple as that, but that's the basic idea of what they're achieving here.

What they think they can achieve is like a windmill turns and then it heats up water, which is then used to, generate energy to somehow turn the windmill again, various complicated mechanisms like this. This is obviously not possible because it would violate the first law of thermodynamics. Remember the first law? The first law says that the increase in internal energy of a system is equal to heat added plus work done. Heat added plus work done, that's total energy. If you are saying that you are going to keep a system running perpetually forever and extract useful energy out of it, that means you're somehow increased, the total amount of energy in the system.

That is not possible. Energy cannot be created or destroyed. You can't just create energy out of thin air. That's essentially what the first law is saying. Perpetual motion machines that claim to produce energy that's usable and still run themselves forever are somehow more than 100% efficient. They're perpetually maintaining their own motion plus producing an output of energy. Impossible. Cannot be done.

Now, the second form of perpetual motion machines are somewhat less, not quite as bad, but still impossible. These are those that violate only the second law. Now, this kind of perpetual motion machine would be one that extracted all of the internal energy of a system and converted into mechanical energy. So this would be a violation of the second law. An example of such a perpetual motion machine would be

one in which somehow water was heated up by some process and then the machine was able to extract all of that additional thermal energy from the water and convert it back into kinetic energy, to convert it back into motion. That is not possible. It's not because it violates the first law. That violates the second law.

Such a perpetual motion machine would require, sorry, a 100% efficient refrigerator or a 100% efficient heat engine, neither of which are possible. So you cannot have a perpetual motion machine. Anyone who claims to have a machine, which can run forever, and or produce usable energy,

is either diluted or line. it is not possible. It violates the basic laws of thermodynamics. Transferring energy. Now, there are three main ways that energy can be transferred from one place to another. Specifically heat energy, we're referring to now. These are conduction, convection and radiation. Conduction refers to the transfer of thermal energy that occurs when a temperature difference exists between single isolated objects. So think of a really hot piece of metal touching your skin.

These are single isolated objects, although they must be in contact with each other for this to work. Basically, conduction occurs as the hot substance, which is the metal rod, has molecules that are vibrating or moving around very rapidly. That's what it means to have a high temperature. When the rod is brought into contact with my skin, those molecules that are moving very fast bump into the molecules in my skin. And as they do so, they confer kinetic energy onto my skin molecules, which then begin to vibrate more rapidly. And so as this occurs more and more times, gradually, the molecules in my hand acquire more kinetic energy, start moving around more quickly, and therefore my hand heats up. Similarly, the molecules inside the hot metal rod, if they've increased the kinetic energy of the molecules in my hand, must have lost an identical amount of kinetic energy. And so the rod cools down.

So you can think of it like the fast-moving balls representing the molecules. molecules and atoms in the rod, bashing into the slower moving balls, or molecules, in my hands. And the faster moving balls are slowing down, the slow moving balls are speeding up. And everything tends towards an equal speed, which is, as we know, the same as saying in equal temperature, and that refers to the situation of thermal equilibrium. Now, the greater the temperature difference between the two objects, the more rapidly conduction occurs. So the more rapidly, the slow-moving. molecules are increased in kinetic energy and the more rapidly the faster moving

molecules are decreased in their kinetic energy. The rate at which conduction occurs also increases with the area of contact between the two surfaces. And this is important because area is what determines the rate of conduction but remember that total mass or total amount of substance is what determines heat capacity. So transfer of heat is highly dependent upon surface to volume ratio. surface area to volume ratio decreases as an object becomes more massive. And the reason for this is fairly intuitive, perimeter is similar to surface area and that it increases to the power of two.

It's length times width. So it's X to the power of two, if you like. Volume is length times width times height. So it's X to the power of three. As you increase X, say, which is the length of something, surface area is only increasing to the two, to the power of two, volume is increasing to the power of three. so volume increases more rapidly than surface area.

And that means that your total specific heat capacity, which is dependent upon volume, is increasing much faster than your total surface area, and hence your total ability to conduct that heat away. That is why big objects tend to have a latency in that they take a long time to change in temperature. Now, somewhat surprisingly, air is actually a very good insulator. Air does not conduct heat very well.

For example, you're better putting a can or bottle of drink, into an ice bucket than you are in a bucket of cold water. Because if you put it in an ice bucket, the pockets of air that exist between the ice will help to trap in the heat, I should say trap in the energy inside the... Well, actually, it will prevent the energy from outside coming in and warming up your drink. Whereas if you put it in a bucket of cold water,

the water conducts the heat from outside in more quickly than the air does, and so your drink will actually warm up more quickly. Okay, so that's conduction, molecules hitting other molecules. Convection is the second means of energy transfer. Convection is the transfer of energy by the motion of fluids from one place to another. This generally occurs due to changes in density. So hot water and hot air and most fluids are less dense than cold air, and so they tend to rise away from the heat source.

Think of the old adage, warm air rises. That's the reason why. Warm air or warm water becomes less dense. So it expands, as it expands, it's lighter than the cooler water or the cooler air, and so the warmer air or water moves up away from the source of heat, and the cooler air or water moves and takes its place. And so you can see if hot water is moving one way and cold water is moving in to fill its place,

you've got the beginnings of sort of a rotation there. And typically what happens is the water will be warmed up by, whatever is heating it up, then it will rise away from the heat source, cool water comes in to replace it, that water then begins to warm up. Meanwhile, the formerly warm water that has moved away from the heat source cools down and then the two packets swap around. So you have this sort of a circular loop and that is called a convection cell or convection current. Water or air also is flowing around being heated up and then cooling off, heated down, heated up and cooling down successively. This happens in the Earth's atmosphere and is responsible for a large amount of weather phenomenon.

It also happens on the surface of the sun, and that's why if you look at pictures of the sun, some areas, it looks kind of mottled and granulated, and some areas are darker and some are lighter, brighter than others. That's because of all the convection cells. Convection cells inside the Earth's mantle are also responsible for volcanic activity, tectonic plates, which move around the continents. So convection is very important in just understanding how heaps of different physical processes work. The third way of transferring energy is radiation. Radiation is pretty simple.

It's just the transfer of energy by electromagnetic waves. Basically light. All objects emit electromagnetic radiation. A lot of people don't actually realize this. You right now, as you listen to this podcast, are emitting electromagnetic radiation. The sun emits electromagnetic radiation. So you emit exactly the same stuff as the sun does. Of course, there's a big difference in terms of the amount.

that you emit versus the Sun, and also the average frequency of the electromagnetic radiation that you emit is lower than the frequency emitted by the Sun. And in fact, humans emit most of their EM radiation in what's called the infrared region of the spectrum, and humans can't actually see that with our eyes. So that's why we don't see other people you know, radiating light. They are radiating light, but we can't see the type of light that they're radiating and that's why we don't see that we don't the sun because it radiates most of its light in the visible spectrum, which by definition is visible to us. So if you ever see pictures of people with a blue outline and red sensors, that's showing you the thermal energy and the emission of radiation that is coming from the person. Now, this leads to an interesting phenomenon called thermal expansion,

which refers to the fact that objects change in size as they change in temperature. Most objects become larger as they heat up, so they elongate. And that's why you need to have things like gaps between slabs of concrete on a pavement, or small gaps in the couplings on bridges or in railway lines to stop them from buckling during hot weather, because these small gaps provide space that allows the metal and other things to expand during hot weather. If they didn't have this, the bridges and railway lines and so on would buckle,

and become more bent. The reason for thermal expansion is because, well, think about it, if an object is increasing in temperature, it means its molecules are increasing in average kinetic energy. And as they're increasing in kinetic energy, it means they're moving around and bumping around more. And this in turn means that they are pushing more strongly on surrounding atoms. So if you're like, it's kind of like the internal pressure,

outward pressure of the object is increasing, and so it expands, it pushes itself outwards. That's the reason for thermal expansion. Water is highly unique in that in part of its temperature range between zero and four degrees Celsius, it actually contracts with warmer temperatures. And this property is crucial to us because life may not exist without it. If water did not expand over this temperature range, lakes would freeze from the bottom up, because the bottom would be a denser and colder part of the lake,

and so it would freeze first and then it would freeze the bottom upwards. and most of the lakes on earth would probably be frozen most of the time and it may have been much more difficult for life to emerge under such conditions. Luckily, however, that is not the case, between zero and four degrees, water expands and so the coldest part of a lake, if a lake's near freezing point, the coldest part of the lake is actually on top. And so lakes freeze from the surface down, and that initial layer of ice actually provides a certain amount of insulation to the water underneath

and helps to keep the water underneath a little bit warm, and so prevents the whole leg from freezing over and killing the fish. So that's one of the many very interesting and special properties of water. In fact, I probably should do a whole podcast just on water because it has so many interesting properties. Okay, so last of all, I look at entropy. You may have heard of entropy before, but what is it? Basically, entropy is a measure of the disorder of a system.

And as I said before, another way of stating the second law of thermodynamics is that that the entropy of a system tends to increase over time. Now, what do we mean by disorder? What is that? Well, basically, the more ordered a system is, the fewer number of equivalent arrangements there are. And this system that we're talking about is at a microscopic level. So we're talking about the different states that the particles can be in. They're orientations, their kinetic energies, their arrangements relative to each other, etc.

That's what we mean by different states or arrangements. order refers to the number of equivalent arrangements there could be. So think of your bookshop, for example. If you arrange your books in, let's say, alphabetical order of the name, the surname of the author, there is probably only one possible arrangement of the books that there could be, one equivalent arrangement. So that is a very ordered system. Whereas if you put the books in, let's say, alphabetical order of the surname of the author,

except that within the letter, like say within all the letter A's, there is no particular order. They're just random within the A's, but A's come before B's, and B's come before C's, etc. That has a much larger number of equivalent arrangements compared to the initial fully alphabetized arrangement. But it's still somewhat ordered, so there are a moderate number of equivalent arrangements. Compare that to, if you just had the books randomly assorted in any old way you liked on the bookshelf, that has a huge number of equivalent possible arrangements and so has a very low amount of order, a very high level of disorder. And this fact is crucial.

There are more equivalent arrangements that are disordered than there are ordered. Even though there are different, say, think of your bookshelf again, there are different ways of ordering books on your bookshelf. Could be by a surname of the author, could be by title of the book, etc. Could be by size of the book. But still, any of those highly ordered arrangements, there's only one or maybe one, a couple of ways you can arrange the books. Even if you add all of those highly ordered arrangements together, there are still hardly any of them compared to the enormous number of possible non-ordered arrangements of the books that you could have. And because ordered arrangements

are greatly outnumbered by disordered arrangements, systems tend to decrease in order over time. And this is fairly intuitive in everyday life. Just think about your bedroom or some room in your house. If you don't make an effort to consciously keep it ordered, it will become more disordered, because there are more states that the room can be in that are disordered than there are ordered. So, you know, think if you have a particular place where you put an object, let's say your laptop. There's one place that it goes, which is the ordered state, but there are heaps of different states that it could possibly go that are not the ordered state. It could go on your bed, on the floor, on top of the bookshelf, anywhere. By sheer probability, over time, left to itself, the system will

tend towards more disordered arrangements. And this is the essential nature of entropy. Entropy tends to increase over time because there are more possible ways of system being disordered than there are of being ordered. It's just a probability thing. So this means that actually when we say that entropy has to increase every time, that's not strictly true. It is possible that entropy could spontaneously increase. It's not fundamentally prohibited. It's just that the probability is so unlikely that it's never going to happen. So entropy also accounts for, we think at least, the arrow of time. Time always seems to go in only one direction.

Glasses smash on the ground. You never see a splinters of glass coming up, coming together, and forming a whole piece of glass. You never see divers coming up out of the water and all the water moving back into its place. Things like that don't happen. And that's all just a manifestation of entropy. there are more disordered states than ordered states, and so things tend to increase in disorder over time. And this is why we think that time only goes in one direction.

Now, I should also point out that isolated pockets of increasing order are possible, but only if they increase the entropy of the surroundings by more than their own entropy is decreased. And life is a classic example of this. So clearly life forms, particularly humans and mammals and other, complex life, are immensely complicated. And so you might say, well, how did we come about spontaneously if entropy is supposed to be increasing? The answer to this is that the decrease in entropy within life forms is possible only because we increase the entropy of our environment by far more than our own entropy is decreased. And the only way we can do that is by taking an energy

from our surroundings. And in fact, the main source of all the energy for all life on Earth is the sun. So basically, all life on earth is decreasing its entropy, so increasing its order, and it's able to do so because of a massive free lunch of energy coming from the sun. So all of the extra order that you see on earth comes from a much larger decrease in order or increase in entropy that occurs inside the sun all the time. So that is how life is possible in spite of the second law of thermodynamics. And that's all I have today for thermodynamics. And that's all I have today for If you enjoyed this podcast, please help to spread the word by posting a positive review on iTunes. I still haven't got any positive reviews yet, so I'd really appreciate it if you would put one on,

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