Some thoughts about life on Earth – the 2nd Law of Thermodynamics, Peak Oil and transition economies.

What is life? Difficult to define, but let us take as a working definition that a living creature is some agglomeration of molecules which succeeds in maintaining a lower entropy than its surroundings for a significant period of time. What is entropy? Entropy is a measure of how “special” a particular arrangement of molecules is – the lower the entropy, the more “special”.

To illustrate this concept of “special-ness”, imagine first a set of red and blue gas molecules, a hundred of each say, bouncing around in a room. Which is more likely, that all 100 red molecules will be in one half of the room and all 100 blue in the other half, or that some roughly even mixture of red and blues will be present in both halves? The second is more likely, less “special” therefore, but why? The answer is that there are many ways of arranging the molecules to have “some roughly even mixture” – a great many pairs of molecules can be swapped without making a difference. However, with the perfect red and blue split, if any molecule is swapped with a partner in the other half of the room, then each half gets “contaminated” with one molecule of the “wrong” colour – such a swap does make a difference.

Now we are able to state the notion of entropy precisely – the entropy of such a set of molecules is a number that is large when there are many ways of swapping pairs of molecules and getting the same overall state and small when there are few ways of swapping them and getting the same overall state. Explicitly, an entropy S is found using Boltzmann’s equation, S = k log W, where k is Boltzmann’s constant and W is the number of ways of swapping the components of a state without making an overall difference to that state.

Now that we understand what entropy is, we can understand why hot things tend to get colder and cold things tend to get hotter. Firstly, what is temperature? Temperature is a measure of how violently the molecules in an object are jiggling – very violently if it is hot, not so much if it is cold. Just like with the locations of the red and blue molecules, there are far fewer ways for all the molecules in one place to be jiggling more than all the molecules in another place, than there are for them all to be jiggling with roughly the same vigour. That means that as these molecules continue bumping into one another, one tends to end up in a state where they are all jiggling roughly the same amount, simply because this is overwhelmingly more likely. Hence, upon mixing hot and cold water together and waiting, one soon ends up with lukewarm water.

There is a fancy name for all this jiggling – The Second Law of Thermodynamics. This states that the entropy of a closed system always increases. Now that we know what entropy is, we can also understand why this law is correct – it’s because entropy is a number that’s low when a system is “special”, and “special” states, like separated red and blue molecules or separated hot and cold water, tend to become “un-special” states, like equally mixed red and blue molecules or lukewarm water, because there are more ways to be “un-special” than to be “special”.

Life, such as you or me, is clearly in a “special” low entropy state in which many differentiated parts are performing separate functions – upon swapping the molecules of your heart and brain for example you wouldn’t be in the same overall state – you would soon be dead! Hence my working definition of life was something that manages to remain in such a “special” state of for a protracted period of time. How does life do this without violating the 2nd law? The answer is that our bodies are not closed systems – we take in low entropy stocks of chemical energy – food – and emit high entropy waste – heat. This waste heat is “un-special” energy that increases the entropy of our surrounding by more than the entropy inside our bodies goes down. Hence the total entropy, that of “us + surroundings” increases – we do in fact obey the 2nd law.

This low entropy food stock we require exists thanks to photosynthesis – plants use the low entropy light energy supplied by the sun to manufacture their own food, sugars, which animals can eat. So ultimately, life on Earth is possible because the sun provides a stable supply of low entropy light energy. This energy from the sun is “special” because the sun is “a bright spot in a dark sky” as Roger Penrose puts it, in a very interesting chapter on the 2nd law from his book The Road to Reality. Low entropy solar energy is later returned to space as high entropy waste – the black-body radiation emitted uniformly from the Earth’s surface.

Now, what does any of this have to with economics? Well, for most of its history life on earth has lived like this, on sunlight alone. Every now and again, some of the low entropy energy captured from this sunlight by plants and stored in their bodies and the bodies of animals would become buried deep underground. Over time, this buried sunlight became compressed to form oil and coal. About 200 years ago, an enterprising and relatively new species began to recover this buried sunlight in significant amounts and liberate its highly concentrated stock of low entropy energy – the species of course was us, human beings. This gave us the capacity to power all manner of machines and develop an industrial civilisation that currently supports around 7 billion of our kind.

However, the supply of low entropy sunlight energy laid down during the many millions of years before our arrival is not unlimited, and soon we may have to live on sunlight again, just as practically every other organism does today, and has done throughout Earth’s history. There are causes for concern here – feeding 7 billion people is no simple task and moreover is a task that currently depends on oil, as Philip Smith has pointed out in chapter 6 of his and Manfred Max-Neef’s book Economics Unmasked:

The highly productive grains developed in the so called “Green Revolution”, which both led to and made possible the greatest explosion of population in humankind’s history, can be grown thanks only to large inputs of agricultural fertilizers and pesticides. These are industrial products, the manufacture of which depends directly on the readily available [low entropy] energy in oil. This translates into several billion people being alive at this moment because of the temporary extra energy input (beyond that of sunlight) of petroleum. When this is depleted, there will be no way to feed the entire population of the Earth, and mass starvation will be inevitable.

Assuming the above statement is correct, that locally sourced organic produce cannot feed our global population [a topic I mean to research soon and write a post about], perhaps the following plans are needed:

  1. Cut back on our use of fossil fuels for non-essential activities, to buy ourselves as much time as possible, during which we could:
  2. Try to gradually bring down our current population to a level that will be sustainable for a future human civilisation running on sunlight alone and:
  3. Train an economics profession willing and able to research what this sustainable level might actually be and how to best provide for it, based on the laws on thermodynamics and not on vague appeals to some hoped for “market innovation” of the future, which nobody can accurately predict.

Signs of either 1, 2 or 3 happening soon are not particularly encouraging. Hoping for a new (and currently un-proven) technological fix to arrive just in the nick of time, in the form of say nuclear fusion, while we continue full-steam ahead to wantonly consume our low entropy stock-pile of fossil fuels, does not strike me as a credible alternative “plan”. Gambling the lives of billions on the mere crossing of ones fingers is a highly morally objectionable way to run any economy.

All this should be cause for serious concern and serious reflection upon the behaviors our current economic systems incentivise – especially amongst those of us who care about the problems our grand-children could face, or the sort of world they will be left to inherit from us. To make immediate and consistent use of our currently dormant capacity for foresight is perhaps the most “economic” choice now available to us.


~ by freedomthistime on July 6, 2011.

2 Responses to “Some thoughts about life on Earth – the 2nd Law of Thermodynamics, Peak Oil and transition economies.”

  1. Hi David

    Just came across your blog after seeing your post on Positive Money. Will spend some time over the next few days /weeks to fully digest what you’ve written.

    Glad to see a scientist write on these topics. I’ve written some similar pieces on my blog here:

    In particular you may appreciate the post on “Is economics a real science”.

    Incidentally, have you read any Frederick Soddy? The importance of energy on growth, and the true role of money was spelled out by him nearly 90 years ago:

    • I’ve heard about Frederick Soddy through some of Herman Daly’s essays (see my post on “ecological economics”) – he’s on a long list of people I need to get around to reading at some point! Thanks for the link to some of his lectures 🙂

      I took a quick look at your blog just now and will probably need more time to “fully digest what you’ve written” too! Once I do, I’ll leave some thoughts there.

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