physics thermodynamics biology
Definition
Free Energy
Free Energy is the portion of a system’s internal energy that can be converted into work at constant temperature and pressure. In the context of thermodynamics, it represents the “available” energy that can be harnessed to drive processes such as metabolism, mechanical work, or computation.
Thermodynamic Context
Free energy is inversely related to entropy. In a system far from equilibrium, where entropy is low, free energy is high. As the system approaches equilibrium—the state of maximum disorder—its free energy decreases until it reaches zero.
Obs
The relationship between energy, entropy, and work lies at the heart of both thermodynamics and life. Work can only be performed by a system in disequilibrium, such as when there is a gradient in pressure, temperature, or chemical concentration.
Biological Significance
Living organisms must continuously import free energy (typically through the metabolism of organic molecules or photosynthesis) to maintain their dynamic stability. This energy is used to:
- Drive metabolic pathways (e.g., the reverse Krebs cycle).
- Maintain proton gradients across mitochondrial membranes.
- Perform cellular construction, repair, and replication.
- Execute biological computation (e.g., gene regulation and neural activity).
Variational Free Energy
In neuroscience and information theory, the concept is extended to the free energy principle. Here, “variational free energy” serves as a proxy for “surprise” or prediction error. While the thermodynamic and information-theoretic definitions are distinct, they are functionally linked: minimising variational free energy is the computational strategy living systems use to secure their thermodynamic free energy and ensure their continued existence.