Confusion and disorder

By Vic Arcus 01/03/2010 2


Confusion and disorder go together in many respects. Politically…. Socially…. disorder and confusion are firm friends. But I would like to speak about disorder from a scientific point of view because in this respect as well, there tends to be confusion.

And yet, disorder (or entropy) is one of the most important concepts in science. Peter Atkins (Oxford chemistry professor and author) cites the second law of thermodynamics (which is about disorder) as the reason why everything in the universe happens. And Einstein agrees: “It is the only physical theory of universal content which I am convinced will never be overthrown.”

So it is worthwhile making some attempt to get to grips with disorder (or entropy) whilst avoiding confusion.

We see a tendency for things to become more disordered in our everyday lives. Somehow the house does not stay tidy, nor does my desk. The glass which falls on the concrete shatters into pieces. My car deteriorates with rust and fading paint. It’s natural for things to become disordered. Beautiful snowflakes melt, sugar dissolves in tea. For humans, the passage of time is cruel and we get old, our bodies deteriorate. More disorder. Yep… things get worse. Well, that’s the second law of thermodynamics in a nutshell.

More formally: Spontaneous processes go from relative order to relative disorder. The scientific term for disorder is entropy and so an equivalent statement is: that all processes involve increasing entropy. I like the concept that energy and matter are dissipating when disorder is increasing (I’ve borrowed from Peter Atkins, here). When the glass breaks, the glass itself spreads out into tiny pieces (its mass dissipates) and there is often quite a loud crack. The loud crack is energy dissipating in the form of sound.

But have I caught myself in an apparent contradiction? I look around my garden and it seems that the natural world is full of beautiful and complicated structures which are ordered. The fronds of a ponga fern are extraordinary spirals, the symmetry in starfish, the wonderful complexities of our own bodies – our brains are so complicated, we do not understand how they work! Life appears to be fantastically ordered. Even an E. coli cell has molecular machinery which perform incredible functions. Where did all this “order” come from, if one of the fundamental laws of the universe says that natural processes are driven towards increasing disorder? (Don’t worry, I’m not going to cite a benevolent, omnipotent designer at this point). This conundrum requires a simpler explanation, which reconciles the second law of thermodynamics with the order in the machinery of life.

If life’s machine were an engine, then it needs fuel to make it run. And the fuel is a source of energy. The process of burning this fuel (in our cars, say) dissipates lots of mass and lots of energy. Think of a tank of petrol turning into carbon dioxide, carbon monoxide, lots of heat, lots of noise. Provided that the sum total of this “dissipation of mass and energy” is greater than the “order” created by the work that the engine does, then you’re OK as far as the second law of thermodynamics goes. Incidentally, this is why we can’t get an engine which is 100% efficient, because the second law says that we must “dissipate” some of the mass and energy and not turn it entirely into productive work.

So it is the same with life. To construct life’s machinery, we need energy. We get this from food, plants get this from nutrients in the soil and sunlight. And in using all this energy, some must be dissipated, spread out, ultimately lost so that we don’t offend the 2nd law. For life, where does this energy ultimately come from? We need to work our way down the food chain to find out. Our food (and energy) comes from plants and animals. Plants get their energy from nutrients and sunlight. Animals eat other animals and plants. Plants get their energy from… sunlight. So sunlight is very, very important for life. It one of the fundatmental sources of energy  which allows the construction of ordered things like organisms. There is another, hidden source of energy on earth and this is in the earth itself. Many bacteria live by using the energy stored in minerals in the earth’s crust. These bugs are called chemolithoautotrophs! “Chemo-” because they get their energy from chemicals in the environment. “-Litho-” because these chemicals are inorganic, usually from the earth’s crust. And “-auto-” because they get their carbon from carbon dioxide.

The inorganic chemicals which these bugs use as a source of energy are the product of chemical reactions in the earth’s crust. These reactions are ultimately driven by the very hot core of our planet. And the core is hot because of gravity! The mass of the earth and its gravitational energy heats the earth’s core and drives chemical reactions in the crust. This chemistry is dramatically visible when volcanoes erupt or mud boils. In a similar way,  the sun’s energy is driven by fusion reactions which take place due to the vast pressures inside its core. This is also due to huge gravitational forces inside the sun.

So to overcome the 2nd law of thermodynamics and create life, we need a source of energy. This energy comes from the sun and the chemistry of the earth. Both energy sources are ultimately the product of gravity. Gravity gave us life. Everything else is either cooling down (dissipating energy into the surroundings) or falling apart (dissipating mass).

Some post-notes on entropy:

1. To be confused about entropy is quite all right. Here’s what the great James Lovelock (author of Gaia) said:

“Few physical concepts have caused as much confusion and misunderstanding as has that of entropy.”

or this from the mathematician John von Neumann:

“You should call it entropy, because nobody knows what entropy really is, so in a debate you will always have the advantage.”

For a combative, controversial and compelling argument for the power of the second law of thermodynamics and its central place in our understanding, watch this lecture by Oxford chemist Peter Atkins. My favourite quote from this lecture is:

“No other law of science has contributed more to the human spirit”

[googlevideo]http://video.google.com/videoplay?docid=5497989647634565004#[/googlevideo]


2 Responses to “Confusion and disorder”