The Second Law Of Thermodynamics Interpreted For Open Systems

If ecosystems were isolated, no energy or matter could be exchanged across their boundaries. The systems would spontaneously degrade their initially contained exergy and increase their entropy, corresponding to a loss of order and organization, and increase in the randomness of their constituents and microstates. This dissipation process would cease at equilibrium, where no further motion or change would be possible. The physical manifestation would ultimately be a meltdown to the proverbial "inorganic soup" containing degradation products dispersed equiprobably throughout the entire volume of the system. All gradients of all kinds would be eliminated, and the system would be frozen in time in a stable, fixed configuration. The high-energy chemical compounds of biological systems, faced suddenly with isolation, would decompose spontaneously (but not necessarily instantaneously) to compounds with high-entropy contents. The process would be progressive to higher and higher entropy states, and would, in the presence of oxygen, end with a mixture of inorganic residues— carbon dioxide, water, nitrates, phosphates, and sulphates, etc. These simpler compounds could never be reconfigured into the complex molecules necessary to carry on life processes without the input of new low-entropy energy to be employed in biosynthesis. An isolated ecosystem could, therefore, in the best case sustain life for only a limited period of time, less than that required from the onset of isolation to reach thermodynamic equilibrium. Observations of properties could not be made, only inferred, because observation requires some kind of exchanges between the system and an observer. There would be no internal processes, because no gradients would exist to enable them. There would only be uninterrupted and uninterruptible stillness and sameness which would never change. The system would be completely static at thermodynamic equilibrium. Thus, in a peculiar way, isolated systems can only be pure abstractions in reality, submitting neither to time passage, change, nor actual observation. They are the first "black holes" of physics, and the antithesis of our systems plus their environments which are the core model for systems ecology. No ecosystem could ever exist and be known to us as an isolated system.

The second law of thermodynamics, though open to question, still retains its status as one of the most fundamental laws of nature. The law has been expressed in many ways. As indicated above: entropy will always increase and exergy will always decrease for an isolated system. Time has one direction. Tiezzi (2003b) concludes that entropy applied to far from thermodynamic equilibrium systems is not a state function since it has intrinsic evolutionary properties, strikingly at variance with classical thermodynamics. Work capacity is constantly lost as heat at the temperature of the environment that cannot do work. It implies that all processes are irreversible. The total reversibility of Newton's Universe (and even of the relativity theories) is no longer valid (Tiezzi, 2003a,b, 2005). The introduction of irreversibility has, however, opened for new emergent possibilities. Without irreversibility there would have been no evolution (Tiezzi, 2005), that is one of the most clear examples of a totally irreversible process. The directionality of ecosystems that will be discussed in Chapter 4, is also a result of the second law of thermodynamics. The second law of thermodynamics and the irreversibility of all processes have given the world new, rich, and beautiful possibilities that a reversible world not could offer.

That is the current dogma, at least, and it is probably true. However, it is useful to at least briefly consider the attributes of a reversible world. Time travel would be possible; this has been amply fantasized in literature. There would be no "evolution" in the sense we understand, but returning to former states could be seen as quite interesting and refreshing, especially if those states were more desirable, let us say further from equilibrium, than their current alternatives. Beauty and rich possibilities—what could be more enriching and beautiful than restoration of former systems, and lives, after wars or other privations, have driven them nearer to equilibrium. Reversibility could produce quite an interesting world, from many perspectives, replacing the humdrum grinding reality of movement toward equilibrium following exergy seeding.

The decrease in entropy or the increase in the eco-exergy in the biosphere depends on its capacity to capture energy from the sun and to retransmit it to space in the form of infrared radiation (positive entropy). If retransmission is prevented, in other words, if the planet were shrouded in an adiabatic membrane (greenhouse effect), all living processes would cease very quickly and the system would decay toward the equilibrium state, i.e. toward thermal death. A sink is just as necessary for life as a source to ensure the temperature that is required for carbon-based life.

Morowitz (1968) continues that all biological processes depend on the absorption of solar photons and the transfer of heat to the celestial sinks. The sun would not be an exergy source if there were not a sink for the flow of thermal energy. The surface of the Earth is at a constant total energy, re-emitting as much energy as it absorbs. The subtle difference is that it is not energy per se that makes life continue but the flow of energy through the system. The global ecological system or biosphere can be defined as the part of the Earth's surface that is ordered by the flow of energy by means of the process of photosynthesis.

The physical chemistry mechanism was elegantly described by Nobel Prize winner Albert Szent-Gyorgy as the common knowledge that the ultimate source of all our energy and negative entropy is the sun. When a photon interacts with a particle of matter on our globe, it raises an electron or a pair of electrons to a higher energy level. This excited state usually has a brief life and the electron falls back to its basic level in 10-7-10-8 s, giving up its energy in one way or another. Life has learned to capture the electron in the excited state, to uncouple it from its partner and to let it decay to its fundamental level through the biological machinery, using the extra energy for vital processes.

All biological processes, therefore, take place because they are utilizing an energy source. With exception of the chemotrophic systems at submarine vents, the ultimate energy source is the solar radiation. Morowitz (1968) notes that it is this tension between photosynthetic construction and thermal degradation that sustains the global operation of the biosphere and the great ecological cycles. This entropic behavior marks the difference between living systems and dead things.

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