New Criticals

So that’s how the laws of thermo act as an enabling constraint on the energetic conditions necessary for life. But I said that organisms are a class of dissipative structure, not just any old dissipative structure. Any material kinetically responding to an energy gradient is dissipative to some extent, but most systems exhibiting this property are not alive (streams, candles, stars, tornadoes and hurricanes...anytime you see an ensemble of matter moving together basically). Dissipative structuring is a necessary but insufficient condition for life. The second way in which the laws of thermo act as an enabling constraint for life involves the generation of molecular complexity to provide the basis for functional information which allows networks of dissipative flows to coalesce into autocatalytic cycles. So now lets start unpacking all that jargon.

If you recall my last post, then you know that chemical changes which result in a greater diversity of molecules always increase the number of available microscopic arrangements of the system, and thus they increase entropy. But nothing guarantees that an ensemble of matter can undergo chemical transformations, and if the chemistry is possible nothing guarantees that the energy input into the system is sufficient to drive the possible chemical changes. This is why being a dissipative structure is a necessary condition for life. In general, for a given set of chemical possibilities, there exists an upper and lower bound for the magnitude of the energy gradient required to direct those possibilities into stable pathways of dissipation. When people talk about “the goldilocks zone” for the distance between a planet and its star required to support life, what they are estimating is the range of temperature differences under which stable dissipative flows are possible with organic chemistry in water. I haven't said much about water yet but it is to intercellular processes what space is to the biosphere, so we'll get there soon.