Bright light

Thermodynamic perspective

This essay will look at living systems in the light of thermodynamics.

Livings systems will be considered as a type of dissipative structures.

Dissipative structures are dynamical systems with structures which flatten out energy gradients in the environment - by degrading sources of potential energy and generating heat.

Burning bright

The basic idea discussed here is that living systems evolve in a way that exploit the resources available to them as rapidly as possible.

Ecosystems tend to evolve by accumulating technology which assist them in:

identifing sources of potential energy and...
utilising those resources for reproductive ends.

As a result of the evolutionary process, ecosystems typically become increasingly adept at identifying and utilising sources of potential energy in their environment.

Self-organising systems dissipate energy

An example of a self-organizing system that is well known for increasing the rate of entropy increase is the vortex that forms when draining liquid through a hole.

This example is one of the illustrations of the "gradient reducing nature of self-organizing systems" used by Kay and Schneider.

Dribble

Vortex

Anyone who's spent much time getting liquids out of bottles is already intuitively familiar with the phenomenon illustrated above.

If you give the liquid a slight spin then a vortex forms - and the liquid comes out much more rapidly.

The turbulent flow finds that it can best dissipate energy if it forms an air channel from the surface of the liquid to the exit hole.

This air channel allows air to flow into the bottle in a continuous stream - so the pressure difference which would otherwise act to hold the water in the bottle is minimised.

In my experiments, creating such a vortex reduced total drainage times by a factor of three - representing a substantial rise in the rate of entropy increase after a slight perturbation has introduced a self-organising system into the bottle.

As Kay and Schneider point out, much the same phenomena plays a role in dissipating energy in the atmosphere - in the form of real tornadoes and hurricanes. Indeed, there's been quite a bit of work on maximum power principles in the field of meteorology.

Work in that area is discussed in more detail here.

Why?

What's the mechanism for the effect? What is it about self-organising systems that leads to them maximising their power throughput?

The main reason for thinking that ecosystems might behave in this way has a conceptually simple theoretical foundation.

This reason the principle applies in biology was first clearly described by Lotka in 1922.

In a competition between two similar populations the group with greater ability to locate and utilise sources of energy is likely to prevail. Consequently we might expect to see a greater rate of utilisation of resources as time passes - as organisms get better at using environmental energy sources - and turning potential energy into offspring.

This essay explores the reason for the existence of the maximum power principle in some more depth.

Generality

Biology is quite a bit different from meteorology. How can the maximum power principle be showing up in in such different fields?

Maybe that's because it's a law of thermodynamics - that applies to all self-organising systems.

This essay explores how widespread the principle is, and the circumstances under which it applies.

The maximand

The self organising systems under discussion here certainly look as though their behaviour is the result of maximising some function. However different authors have proposed different maximands.

Here I discuss the validity of the various proposals for exactly what is being maximised in these systems.

Supporters

Kay and Schneider explored a number of the ideas discussed here - in 1994.

They wrote, for example:

ecosystems develop and select energetic pathways that strive to degrade as much of the energy available to them as possible.

This perspective appears to invert the conventional wisdom that living systems are attempting to create order - partly in the form of copies of their genome - rather than disorder. However - as we will come to see - these activities are rather fundamentally interrelated.

Another supporter seems to be Michael J. Russel:

What does Life do?
It responds electrochemically to geochemical and photochemical tensions on Earth by attempting to resolve them, remaking itself in the process that it might create a greater overall disorder. Or in the words of Simon Black (2000) -"energy uses an organism as a mechanism for self- dissipation."

Burning bright - or burning long?

The rate at which the resources can be utilised can be a factor which influences the competitiveness of a population.

If two populations expand into an environment which has plentiful resources, the population that can most rapidly translate the energy into offspring is likely to wind up with a significant weight of numbers - and this can easily translate into a competitive advantage in any battle for what remains.

Overall efficiency can also be relevant - in times where food is scarse, the future may belong - not to the population that attemps to turn its food into increased population as rapidly as possible - but rather to those that maintian a low population size and conserve their food supplies.

These strategies are usually mutually exclusive - burning brightly is usually not going to produce a light that lasts for such a long time.

I believe these strategies can usefully be seen as the result of optimising over different time periods. The first is more short sighted - while the latter takes a more long term view.

In the context of this essay the question of whether nature is "burning bright", or is "burning long", boils down to the question of whether she is maximising burn rate - or is creating maximal eventual disorder. It seems likely that the truth lies somewhere in between these two extremes.

Maximising order - and maximising disorder

Evolutionary biologists often judge the "worth" [1] of biological features, by considering to what extent they contribute to the copying of the genotype responsible for that feature.

In thermodynamic terms, that can be seen as a rather simple approximation of the quantity of order condensed from the environment into its own tissues.

The approach here suggests another metric - namely the extent to which a feature contributes to degrading the various sources of energy in the environment - increasing overall entropy - and creating disorder.

These metrics are clearly closely related - since in the process of creating the order present in those genomes, a great deal of disorder will inevitably need to be created somewhere.

Attempts to maximise order actually maximise disorder

A thermodynamic analogy may help to see why maximising order in one place has the effect of maximising the total disorder:

Imagine you have a fridge, which you want to keep cool. The colder you make it, the more energy it takes to maintain its temperature in the face of ambient heat from the environment. Similarly if you want to make the fridge larger, it will take more energy to keep it cool - since the rate of heat loss through the surface will increase - due to the increased surface area.

In this analogy, the cool fridge represents the order in a living system. Attempts to increase this appear to inevitably result in more disorder elsewhere.

It seems that any dynamical system that attemps to create order in one region will inevitably wind op doing so by increasing the total entropy. The more order it attempts to maintain, the greater rate at which it depletes the available energy sources.

The thermodynamic view

There are advantages to adopting a thermodynamic stance. It better allows comparisons between individuals from different species - than counting genes does.

Often, counting genes, genomes - or any other reproductive unit - would be a rather pointless exercise - since comparions between species would make little sense.

To those unfamiliar with the idea, it might seem odd to describle the "purpose" or "function" of a "designoid" system in thermodynamic terms - rather than in terms of making more copies of genes - but it seems to me that such a description more accurately represents what is fundamentally going on.

Such thermodynamic metrics - in common with the more familiar reproductive ones - can both be applied over different timescales.

Since different elements of a system may be attempting to optimise over different timescales - constructing a single function that is being optimised may prove challenging.

The relationship between created order and environmental disorder suggests a flip-side to approaches involving measuring reproductive success.

Rather than attemping to estimate the extent of the order created by a living system - you could see to what extent it has made use of the available energy sources.

Looking at the state of sources of environmental energy may sometimes be more practical than attemping to assess the order created by an ecosystem.

Is life creating order - or disorder?

Is the creation of disorder by ecosystems a "by-product" of their striving towards order?

Or can we follow [Kay and Schneider] - and say that ecosystems "strive to degrade as much of the energy available to them as possible"?

It seems established that attempts to create order will necessarily increase overall entropy.

Similarly it seems that one of the best ways to increase entropy - in the long term - is to introduce a complex living system into the environment.

The thesis that living systems are attempting to maximise total entropy is "paradoxically" very similar to the one that they are attempting to create maximum local order (by making many copies of their genome).

Overall, I'm inclined to state the goal of living systems in overall thermodynamic terms - and thus to talk about creating disorder - rather than (say) maximising the number of copies of genes created.

Though very similar, the two ideas expressed above are different from one another - and will make different predictions.

I think the thermodynamic expression will eventually be seen as more accurate description of what's going on under such circumstances.

Does life really maximise disorder?

It is not easy to show that life is maximally effective at increasing entropy. However it seems likely that it will be much more effective than most of the alternatives - provided not too short term a view is taken.

Nuclear explosions might well create a rapid local entropy increase faster than a typical living system would manage - but the effect is localised - and short lived. A living system ought to be able to do a much better at increasing entropy in the long term than such an explosion.

Inefficiencies

The idea that ecosystems maximise their rate of energy dissipation does not necessarily mean that they are coming to utilise their energy more efficiently.

Indeed, perhaps rather the opposite: it's been argued that the process of degrading available energy sources as rapidly as possible will inevitably involve a substantial degree of waste - since utilising energy rapidly and utilising it efficiently are different goals that will inevitably conflict.

However, it can be argued that such "maximum power principles" will result a certain sort of efficiency of a kind - and avoidance of some sorts of "pointless" waste.

One possible objection to the idea that populations come to utilise their resources with increasing efficiency is that populations are fundamentally lacking in harmony - by virtue of being divided into discrete individuals with conflicting objectives.

The tragedy of the commons, greedy predation, "driving genes", within-species conflict and runaway sexual ornamentation can all be seen as being counter-productive - from the point of view of overall efficiency - and it might be that barriers such as these will prevent energy from ever being utilised very efficiently.

While I don't regard this objection as very serious, I discuss it in more detail here.

More to life than power?

Isn't there more to living systems that the power they generate?

What about the possibilty of organisms defeating other organisms on other grounds than their ability to rapidly utilise the available energetic resources?

These are reasonable questions - and they are discussed further here.

Between order and chaos

I hope the ideas discussed here will throw some light on the popular notion of "life evolving to the edge of chaos".

I have a separate document discussing this matter - here.

Progress

Does the tendency of living systems to get better at utilising energetic resources result in a sort of progress.

In this essay, I argue that yes, it does.

The future

The picture painted here of living systems inexorably increasing their power consumption might suggest images of future living systems as explosions - expanding through unoccupied regions at great speed and causing complete destruction in their wake.

I don't mean to suggest that in the future there will also be such emphasis on maximum speed in the short term.

Life has been rather short-sighted in the past.

Part of the reason for the historical short-sightedness is that until relatively recently, saying much about the future was very difficult because the equipment available for building models of the future were very primitive.

Now living systems are becoming much better at understanding their environment and predicting the future - though unfortunately a rapid pace of change is acting simultaneously to make the task more difficult.

Living systems have demonstrated that they can conserve resouces when that's appropriate. Many of the adaptations that become evident when organisms are calorie restricted are evidence of this. However, organisms normally only react to current shortages, and don't do a good job of anticipating future resource shortages.

I hope in the future living systems will do a better job of managing their resources based on future expectations. It might well sometimes turn out to be a better stratgey for living systems to save resources for later - in the hope of persisting for longer.

If "maximum speed" does continue to remain desirable then I do not know how rapidly future generations will be able to expand their horizons - or to what extent they will succeed in utilising the resources that lie in their path - but I fully expect that very impressive feats on these fronts are possible.