Thermodynamicsâholds, I think, the supreme position among the Laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwellâs equationsâthen so much the worse for Maxwellâs equations. If it is found to be contradicted by observationâwell, these experimentalists bungle things sometimes. But if your theory is found to be against the Second Law of Thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.â
You donât have to know or care about Maxwellâs equations to get a sense of what he means. (But just so you know, they are the equations that describe the nature of light, electricity, and magnetism.) The key idea is that the Second Law of Thermodynamics mathematically describes any systemâs loss of energy to its surroundings. It is fundamental to the way the natural world works. Since energy is constantly and continuously spreading out, everything should be winding down to a dead stop. Perhaps you can see why creationists figure that the Second Law means thereâs no way for evolution to add complexity to life. How could any living system get organized, if all its driving forces were continually diluted, spread out into the vast blackness of the universe?
As a mechanical engineer who took a lot of physics, I am fascinated by this particular creationist argument, because it is both scientifically subtle and completely misinformed. Hereâs the most important thing to know: The Second Law applies only to closed systems, like a cylinder in a car engine, and Earth is not even remotely a closed system. Transfers of matter and energy are constantly taking place. Life here is nothing like a perpetual motion machine, but neither is it like a ball rolling inexorably downhill.
There are three main sources of energy for life on Earth: the Sun, the heat from fissioning atoms deep inside Earth, and the primordial spin of Earth itself. These sources provide energy throughout the day. The Sun provides the most energy. Itâs a fusion reactor releasing 10 26 Watts every second (10 26 Joules). Earthâs core also provides energy in the form of heat. The spinning of our planet keeps shifting the energy inputs and adds acceleration to the wind and the waves. So as you can see, the world we live on is not even remotely a closed system. All of our worldâs ecosystems ultimately run on a continual external source of light and heat. Energy has been pouring in from the Sun for over four and a half billion years. Living things ranging from amoebas to sequoias have to find ways to make the best use of all that energy, lest they be outcompeted by other living things that use it more efficiently.
The Second Law sets the boundaries; itâs the rule we all have to play by. Starting with energy to study evolution is a great way to understand life. What do living things do with all this energy? We use it to drive chemical systems that obey the Second Law. But the Second Law comes into play everywhere in your life. When you pedal a bicycle, thereâs a little bit of friction in the chain joints and the bearings that hold the pedal and cranks. The motion makes a little bit of heat. Where does that heat go? It goes into the universe. Really. It dissipates into the environment of the whole world and eventually radiates into space, and thereâs no way to recover it. The tendency for energy to spread out in natural systems might also explain how a kidâs room becomes such a mess.
The modern mechanical world runs on heat, and itâs also bounded by the Second Law. Car engines, jet airplane turbines, and coal-fired power plants all use heat produced by burning to make something spin. The heat comes from chemical reactions. The same is true for us animals. Instead of fire in our bellies, produced by combining carbon fuel with oxygen, we have enzymes that enable chemicals in our food to