Entropy and the Origin of Life

The Second Law of Thermodynamics, Entropy, states that the universe moves from order to disorder.  To the initiate, this would seem to contradict a common observation:  that life systems in general and humans in particular move from a disordered state to an ordered state.  Life seems to move in opposition to entropy.  If the universe moves towards disorder, how, then, does life evolve? These are questions that early researchers in thermodynamics, such as Schrödinger and Prigogine, asked themselves.

In fact, we can see order spontaneously created from disorder around us all the time.  When water starts to go down the drain in the tub, for example, you will see a little whirlpool (vortex in physics-speak) form around the drain.  

Order spontaneously created from Disorder.

Or when a heated solution moves from mere conduction heat transfer to heat transfer through convection cells.  Or when you flick a super-saturated solution of copper sulphate in water and the whole test-tube freezes as the copper sulphate crystallizes. In each case, when faced with a large energy gradient, an organized structure (vortex, convection cell, crystal lattice) spontaneously formed.  So spontaneous organization is not peculiar to life.

What is required in each case is the energy gradient (potential energy from the height of the water in the case of the vortex, heat in the case of the convection cell and concentration in the case of the copper sulphate solution).  The system "wants" to maintain its equilibrium, and the most efficient way it can do this is by organizing itself to dissipate the energy gradient and return to equilibrium.  Order can only appear from disorder if there is an energy gradient to exploit.

In complexity theory, these are known as self-organizing dissipative structures.  "Dissipative" because they "seek" to dissipate the energy gradient and return the system to equilibrium.  These organized systems that spontaneously appear are, in fact, low entropy.  However they only decrease entropy locally, and only in order to more efficiently increase entropy globally.

Moving up in scale, the planet Earth is subject to a huge energy gradient, namely the massive influx of energy from the sun. Recall that exergy is a measure of the quality of energy, the availability of that energy to do something useful.  The energy gradient, or Exergy, is basically a measure of distance of a system from equilibrium.  At equilibrium, exergy is zero. The system (Earth) receives a exergy from the sun in the form of electromagnetic radiation (mainly heat and light).  The system responds in a way to dissipate that exergy, to move it towards zero (equilibrium). 

So taken on their own, humans and other life forms are indeed a reversal in the tendency towards increased entropy.  However, taken within the context of the system as a whole (Earth-Sun system) we are actually increasing the rate of the entropy.  From a thermodynamic perspective, we are self-organized dissipative structures seeking to dissipate the exergy from the sun.

The late Waterloo professor James Kay wrote extensively about non-equilibrium thermodynamics and self-organizing systems.  He cites studies where an overflying aircraft with thermal multispectral analysis capability measures the "canopy temperature" of different ecosystems, including an astroturf field, a mowed lawn, a farmers field, and a complex rainforest ecosystem.  The surface temperature of the rainforest ecosystem was the coolest, indicating that the most complex ecosystem was also the most efficient at using the incoming solar exergy.  The astroturf was the warmest, because there are no life systems (such as photosynthesis) to effectively use the incoming solar radiation.  The rainforest, conversely, had a rich array of life systems to effectively use all the incoming solar energy.

A human being, I have heard said, is an organism that takes perfectly good food and manufactures it into crap.  That is one way we increase entropy.  We also must keep the furnaces of our bodies going, so we constantly generate about as much heat as a 100 W light bulb. On a social level we increase the disorder of the environment around us in order to increase order of our societies.  We take low-entropy bound carbon in oil and release it as very high-entropy gaseous oxidized carbon, for example. We know from the Second Law of Thermodynamics that the amount of disorder we create in the environment is greater than the amount of order we reap (thus, globally, entropy increases).

It’s a great theory and make s a lot of intuitive sense. 

However, I was left wondering:  the energy gradient due to the sun on the planet Mercury is far greater than that of Earth, yet as far as we know, there is no life on Mercury, no super-high level of self-organizing dissipating systems. Same with Venus.  So why only Earth? 

Schrödinger hypothesized that self-organizing dissipative systems only happen within a "window of vitality."  Too little exergy and there is not enough of a gradient to drive the creation of a self-organizing dissipative system.  Too much energy and the system is overcome and becomes chaotic.  But nobody has been able to develop, to my knowledge, any of the science around what the limits of the window of vitality are. 

Until then, the theory of life as a self-organizing dissipative system remains and enticing idea, but it is missing a crucial link.