Austrian physicist Ludwig Boltzmann’s (1844-1906) revolutionary framework of statistical mechanics did not only challenge traditional assumptions about deterministic ‘laws’ of nature but it was also one of the few theories in physics that acknowledged the importance of Darwin’s account of evolution through natural selection. As Boltzmann stated in a famous speech held before the Imperial Academy of Sciences in Vienna in 1886, his age would not be remembered as “the century of iron, electricity and steam” but “as the century of the mechanical view of nature, of Darwin”. In a controversial passage, he then connected his interpretation of the principles of thermodynamics to Darwinian evolution:
“The general struggle for existence of animate beings is not a struggle for raw materials – these, for organisms, are air, water and soil, and are all abundantly available – nor for energy which exists in plenty in any body in the form of heat, be it in an non-transformable state, but a struggle for entropy, which becomes available through the transition of energy from the hot sun to the cold earth.” (italics JM)
Most English translators and colleagues who quoted Boltzmann in English had difficulties with this passage. Almost no one dared to translate “entropy” literally but felt it necessary to give different readings of this concept or to even explicitly correct Boltzmann. Entropy was then replaced with “free energy”, “negative entropy”, “negentropy”, “low entropy”, “enthalpy”, or, more literally (by Alfred Lotka) “available entropy”.
The difficulties with the idea that life struggles for entropy – a concept commonly associated with increasing disintegration and loss of order – are understandable. After all, isn’t life the opposite of disorder, and doesn’t it create regularity and structure? Yet, Boltzmann is clear on this point, and he explicitly rejects the notion that the struggle for existence is a struggle for energy (or matter). In this blogpost, I suggest to take him seriously and investigate what this understanding of life – and its energetic requirements – can tell us about the modes of existence of living beings in this universe, and more specifically about our current historical situation on a planet at is limits. Boltzmann’s notion of a “struggle for entropy” may stimulate reflections on how we use and envision resources, and on how our life (and survival) as humans depends on a multispecies world of beings and on their specific metabolic relationships to their environment.
Competing for what?
Entropy, and the question of why it inevitably increases in any physical system is perhaps the most important feature of Boltzmann’s revolutionary statistical mechanics. In this theoretical framework, entropy is understood as a measure of all the possible microstates within a given macrostate. Statistically, all microstates are equally likely to occur but this very fact limits the probability of certain macrostates: using the analogy of a lottery game, we can say that each number is equally likely to occur in each position (microstate) but the chance of getting all five numbers ‘right’ (macrostate) is very small.
Seen from this perspective, the flow of heat from warm to cold bodies is not a deterministic ‘law’ but a realization of a more likely state – one in which the two bodies reach an equilibrium. This universal trend towards thermal equilibrium, described as the second ‘law’ of thermodynamics predicts that the universe will inevitably have an end and thus reach the most probable of all possible states. In this sense, entropy appears as a measure of disorder and loss of structure, and it has often been discussed whether life itself – and the very existence of living beings – is not in contradiction to the prediction of its continuous increase.
This apparent dilemma did not occur in Boltzmann’s account of biological life. In this vision, life does not contradict the second law of thermodynamics (which is only a statistical law – note that the German language only refers to this ‘law’ as a ‘Hauptsatz’, or a ‘main principle’). Instead, it would be more apt to say that life directly follows this trend towards entropy increase. Life can only occur at an energetic gradient, or a position in which energy flows from one object to another. Boltzmann stresses that our planet is in such a position and we live at a “colossal” temperature gradient between “the hot sun and the cold earth” which dissipates the received heat back into space.
Life on earth has adapted its morphologies to this energetic gradient:
“To make the fullest use of this energy, the plants spread out the immeasurable areas of their leaves and harness the Sun’s energy by a process that is still unexplored, before it sinks down to the temperature level of the Earth, to drive chemical syntheses of which one has no inkling as yet in our laboratories. The products of this chemical kitchen are the object of the struggle in the animal world.”
Why does Boltzmann reject the notion of a struggle for energy?
As long as the sun exists, energy will always be available in abundance and it cannot be the object of struggle or competition itself. However, not all energy can be taken up and distributed such that it becomes usable for living beings. The energy of the sun needs to flow towards a state of higher entropy, thereby enabling organisms to maintain themselves at this gradient.
Citing Hermann von Helmholtz, Boltzmann reminds the readers that all energy sources on the earth – even fossil fuels – are in fact solar energy, if in a stored form. However, in its secondary stage – as the products of the “chemical kitchen” in the leaves of live or fossilized plants it is not directly available to other organisms. Food may be overly abundant but without the necessary physiological adaptations to take up oxygen and ‘burn’ these derived products of solar energy, life is impossible. From this perspective, the ‘struggle for existence’ is not so much a form of competitive division of a limited resource between a given number of (ecological or economic) consumers. Rather, it is a struggle for the adaptations that are necessary to effectively consume the resources in question – and, thus, to increase entropy at the gradient between organisms and their environment.
A given animal population may encounter an unlimited amount of food resources but without the right metabolic or respiratory adaptation, the entropy of the available food source cannot be effectively increased and it will remain useless. The same can occur in human economies: in Europe, it took almost 200 years to establish potatoes as a major food source – the plant’s nutritional energy was already available but the cultural adaptation that enabled Europeans to utilize if (and thus: to break down the plant’s nutrients) was still lacking.
A world of abundance and scarcity
Boltzmann’s struggle for entropy envisions a planet of abundance and it seems to echo Nietzsche’s critique of Darwin and Malthus, which saw the Darwinian “struggle for survival” as something that could theoretically occur but would remain an exception in a world that was characterized by over-abundance. However, neither Nietzsche nor Boltzmann (if for different reasons) downplayed the competitive element that informed the utilization of resources. The world may be a place with abundant energy resources, but not all of those are suited to support organic life. Energy must flow – across physical, chemical, and biological scales, and then across organisms, species and food webs – in order to reach the form in which it can support life. It takes a wide range of lifeforms to bring about the “products of the chemical kitchen” that then becomes available to support new life.
Boltzmann’s emphasis on solar energy as the source resource of all life on Earth sounds timely in our current situation. His reminder that our planet is not a closed system but rather an open one that can only exist thanks to the continuously available energy of the sun is still as topical as in 1886 and the urgency to actually use the abundance of energy we already have may have never been greater.
However, this perspective on energy goes beyond a one-sided focus on quick techno fixes – it highlights how all life on Earth depends on yet other forms of life. To provide the “products of the chemical kitchen” it takes a multitude of different organisms and lifeforms whose mutually dependent productions take place in a wide diversity of ecological and physiological niches. While the necessary energy is already available, we critically depend on the diversity of these different lifeforms ant their ability to produce the livelihoods that maintain the possibility of life and survival on this planet.
The world is a co-production.
Boltzmann, Ludwig. (1886). The Second Law of Thermodynamics (pgs. 14-32). In B. McGinness, ed., Ludwig Boltzmann: Theoretical physics and philosophical problems: Selected Writings. Dordrecht, Netherlands: D. Reidel, 1974.
Gimbel, S. (2024). It Ain’t Necessarily So: Ludwig Boltzmann’s Darwinian Notion of Entropy. Entropy, 26(3), 238.
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