According to thermodynamics, any living organism is constantly exchanging a flux of matter and energy with its environment. As such, the system is in non-equilibrium. In his book What Is Life? (1944), the Austrian physicist and Nobel Laureate Erwin Schrödinger proposed that sustaining life is exactly predicated on avoiding equilibrium: ‘How does the living organism avoid decay? … By eating, drinking, breathing and … assimilating. The technical term is metabolism.’ According to this view, the ultimate equilibrium is death, and thus survival depends on staying as far as possible from equilibrium.

Schrödinger was foremost a physicist, primarily known for his work in quantum physics, where many will know his thought experiment concerning ‘Schrödinger’s cat’ which, paradoxically, may be considered simultaneously both alive and dead. This arose from discussions with Albert Einstein in 1935 about the problems of the Copenhagen Interpretation of quantum mechanics.

Later in life, however, Schrödinger turned to the big and important questions of discovering the essential forces of life and understanding how the field of thermodynamics could help. In those days, the scientific study of the human brain was still in its infancy, and as such not part of Schrödinger’s focus. But since then, neuroscience has made great strides. It has become abundantly clear the brain must be the main driver of how organisms can avoid equilibrium and death. In fact, very recent discoveries have started to cast new light on how brains may even thrive on non-equilibrium; and how turbulent, non-linear brain dynamics help find order in largely disordered environments so as to enhance the chances of survival.

Over the past few decades, brain scientists have focused on how the brain seems to be primarily driven by momentary stimulation from the environment when we engage in specific tasks. Yet, as shown by pioneering research by the American neurologist Marcus Raichle, it has become increasingly clear that the brain is not solely extrinsically driven by information coming from the environment. Instead, the brain is mostly shaped by intrinsic resting-state activity, switching between brain states while interpreting, responding to, and even predicting environmental demands.

This view is supported by the fact that the metabolic energy consumption maintaining the intrinsic resting-brain activity is much larger than that used by extrinsic task-driven demands, such as when watching visual stimuli or solving cognitive tasks. Given that, by some estimates, more than 20 per cent of the total energy consumption is taken up by the brain, which only represents 2 per cent of body weight, Raichle has poetically spoken of the brain’s ‘dark energy’.

Here we propose to fuse the ideas of Schrödinger and Raichle to suggest the idea that the flow of energy between the brain and the environment is driving the non-equilibrium needed to sustain life. This leads to a novel theory of the thermodynamics of mind, a theory that draws on ideas from physics and allows researchers to quantify and characterise the brain processing leading to non-equilibrium with a great degree of precision.

Read more in our Aeon article. More technical details in our Thermodynamics of Mind theory published in TICS.