Conservation of energy (Erhaltung der Kraft)

In his 1847 essay Helmholtz turned to organic beings after the inorganic processes. He described plant processes as mainly chemical, with a store of chemical tension force laid down in plant substance. He named the chemical rays of sunlight as the only living force absorbed during plant growth, according to our knowledge so far.¹ He added that the data to compare the force equivalents lost and gained were still missing. D'Arcy Thompson later quoted a Helmholtz lecture of 1861. Helmholtz allowed that other agents may act in the living body. But forces there, so far as they cause chemical and mechanical influence, must be of the same character as inorganic forces.

Verworn (1899) described Dulong's water calorimeter, in which an animal sits in a double-walled box. When the food's chemical energy is finally transformed into heat, the law says the chemical energy entering as food, counted in calories, must equal the heat the body gives off. Verworn reported that experiments reached this result with all desired exactness, so the law was experimentally confirmed for the living body.² Hill (1926) was more guarded. He called the thermodynamic picture only partial, yet said the certainty with which the principle applies gives firm ground for investigating muscle heat.⁷ Crile (1926) listed among his propositions that the living transformer of energy obeys the same laws as non-living ones.⁶

Authors differed on what the principle is. Driesch (1908) argued that energy is a measurement and nothing else, a gauge of the causality passed between systems.³ He framed this discussion in terms of "entelechy and causality". Leduc (1911) illustrated the law with a suspended weight, where the sum of potential and actual energy stays constant as it falls.⁴ Timiriazeff (1912) called it the highest law of physical science, citing Faraday. He then noted cases where energy seems to use itself up, as with two colliding balls.⁵

Fields, Glazebrook and Levin (2021) build conservation of energy into their minimal physicalism. They treat information and energy as formally equivalent and enforce conservation explicitly.⁹ They say this requires the thermodynamics of classical computation to be represented, and that it makes the thermodynamic cost of memory count at every scale. They add that it enforces a metabolism and cognition tradeoff.⁹