The second law of thermodynamics says energy will go from a place of high concentration to a place of lower concentration. This will mean that there will be less useful energy around, and an increase in entropy, which can be described as ‘chaos’ or ‘useless’ energy. An ordered system is considered to have low entropy.

To take one example, if I want to warm something up on a cold day, I can put some hot stones near it. To make hot stones I need a fire. This changes the wood in the fire from its original form into ashes, releasing energy. I take the hot stones over to the thing I want to warm up, and it does get warm, but the coals get cold. At some point, the heat from the coals is equal to the heat of the article, and no more energy can flow. That system has reached equilibrium.

Another example is if we take a box with a partition in it, and put one gas in one side and another in the other side, the box (or ‘system’) is at a state of high order, or low entropy. Remove the partition and the two gases will flow together, until they are equally mixed. At this point the entropy is at its maximum and the order is at its minimum. The movement of all the particles is at random, but they will tend towards a thorough mixing.

In both of the above examples, we could return things to their ordered state by putting in energy. If I had put the stones back in the fire, they would have heated back up. The important point to notice is that to put order back into the system, work is needed.

The second law of thermodynamics can be demonstrated very easily with the following experiment:

Take 20 dice, arrange them so that all the six's are on top. Now, set a timer going and jumble them up, so that they are in a different order, any order. See how long that took. Now restart the timer and put them back into the original order. See how long that took. Now, I hope that you will find the same as me, and that it takes longer. That equates to more effort. It takes a little work to check each dice and find the Six. So, That is entropy. Nothing more. Nothing less. Order can be created in the universe, but it takes energy to do it. Disorder requires a lot less energy. The other consideration that this brings up is the number of different states a system can be in. If one chooses a particular state (like all sixes in the dice example), then how many different states are there? Obviously a lot more, so even taking into account entropy, it is possible (but very improbable) that a highly ordered state can appear (rolling the dice at random could produce a perfectly ordered state), but the probability is that it won't.

The thing that produces the necessary energy on Earth is the Sun. The energy that we can get from the Sun can be seen by watching a puddle dry up, and can be felt by looking up at the sun on a hot day. We use solar power to make electricity, a form of energy that can be used to create order and information. This doesnot violate the second law. In the same way, life doesn't violate the second law. When considering entropy, one must consider the whole system. The order on Earth increases by life and the uses that Humans put the solar power from, but the Entropy of the Universe increases as a result.

The interest in thermodynamics started after 1798 when James Watt made the first steam engine. This made the idea of the efficiency of engines an important issue. Sadi Carnot showed that engine is dependant on energy going from hot to cold, and that it is less than 100% efficient unless the engine turned so slowly that no practical work could be done.

In 1850, Rudolf Clausius showed that the dissipation of heat from hot to cold causes an assymetry, that cannot be reversed, something is always lost. He followed that up in 1865 by distinguishing between reversible and irreversible processes by introducing the concept of entropy, which is at its highest when no more work can be done.

There are three types of system:

Isolated - Totally insulated from its environment

Closed - Energy but not matter can be transferred to and from its environment

Open - Energy and matter can be transferred to and from its environment.

Clausius showed that in an isolated system entropy always increases

This was expanded on in 1873 and 1878 by Josiah Willard Gibbs, who used the phrase 'equilibrium thermodynamics which describes how entropy increases close to thermodynamic equilibrium

1873/78 Josiah Willard Gibbs à Equilibrium thermodynamics

Free energy - maximum amount of work in a system

Use free energy à increase entropy

1930's Lars Onsager Thermodiffusion, by adding energy, order is maintained. Linear thermodynamics, flux ß à force close to equilibrium

Now then, thermodiffusion. Imagine a hollow dumbell. In it there are two gases. Hydrogen and hydrogen sulphide. Let it reach thermodynamic equilibrium, with both gases mixed throughout the dumbbell. Now apply heat to one side of the dumbbell, and the gases sort themselves out, moving away from equilibrium. The hotter region contains much more of the lighter hydrogen.

1947 Ily Prigogine showed system will dissipate at a minimum.

1971 Far from equilibrium, entropy production high, but system unstable. This may lead to a bifurcation, where the system leaves its steady state and must go into a different steady state. This could be very highly organized, but it must be able to export its entropy to its surroundings. (Glansdorff-Prigogine critereon) doing the same experiment could lead to different but still stable results, and pushed even further the system will reach more bifurcation points, leading to self organising structures that are dependant on the rapid flow of entropy, and because they need to dissipate this away, these are called dissipitive structures.