The astrophysicist Chaisson (2001) has proposed an interesting link between energy and complexity. Organisms can be viewed as dissipative structures: Ordered objects whose structure can be maintained thanks to a steady input of high-quality energy. The free energy flow density (ɸ) necessary to sustain such a non-equilibrium structure is a measure of complexity. It can be expressed in erg per second per gram or, more commonly, in mW per kg (1 erg = 107 joule). The free energy flows are on earth supplied almost exclusively by solar radiation. It is possible to make estimates of the ɸ-values for different systems on earth and the results are shown in the Figure below. It seems that ever since the Big Bang, which started off our story of the universe, complexity measured in this way has been continuously increasing. After early life forms like the archaebacteria in the heat gradients on the ocean floor, an important step towards higher complexity was made with the advent of photosynthesis, the biological mechanism to convert solar energy into chemically stored free energy (ɸ∼0.1 W/kg-biomass). Most animals have ɸ-values in the range of 1 to 10 W/kg-biomass, depending on their activity. Birds operate at an order of magnitude higher than reptiles, which gives this measure some intuitive appeal. The human body dissipates free energy at a rate of about 1 W/kg-biomass, but if you are bicycling it is a factor ten higher – so complex is bicycling in this definition. An astounding increase in free energy density flows happened in the industrial age, with ɸ-values over 100 W/kg-biomass per person. If measuring the free energy density per unit of mass of equipment, going from organic to technological systems, there is a further increase to ɸ-values in the order of 1,000–100,000 W/kg. The most extreme densities are realised in military equipment and microdevices and nanodevices.

 

Figure Estimated values of the free energy flow density in a number of systems (based on Chaisson 2001).

Literature

Chaisson, E. (2001). Cosmic evolution – The rise of complexity in nature. Cambridge, Mass, Harvard University Press