The thermodynamic phase transition hypothesis of ageing: Entropy production and a proposed extension to Strehler's postulates.

Ageing is a multifactorial biological process whose comprehensive understanding requires integrative frameworks bridging biology, physics, and complexity sciences. Despite major advances in identifying molecular mechanisms, a unifying physical principle capable of explaining the progressive loss of systemic stability and the emergence of degenerative diseases remains elusive. In this hypothesis paper, we integrate classical ageing biology, including Strehler's postulates and the Hallmarks of Ageing, with principles from non-equilibrium thermodynamics and complex systems theory. The organism is interpreted as a dissipative structure maintained far from thermodynamic equilibrium, where entropy production is proposed as a candidate physical marker of biological age and may behave as a Lyapunov-like quantity reflecting system stability. Within this framework, ageing is hypothesised as a progressive loss of dynamic robustness that may culminate in a biological phase transition, understood as a transition between dynamical attractors, toward degenerative disease states. Building on this foundation, we propose a fifth postulate that extends classical ageing theory and defines ageing as an emergent property of nonlinear complex systems operating far from equilibrium. This conceptual framework, while requiring further formalization and empirical validation, may provide a bridge linking ageing, longevity, and disease, and suggests new directions for interdisciplinary research.