What is Life?

Abstract: Since Schrodinger's \emph{What Is Life?}, the physical basis of biological organization has been understood in terms of the interplay between matter, energy, and information. Subsequent developments in molecular biology, information theory, nonequilibrium thermodynamics, and evolutionary theory have clarified how hereditary information is stored, maintained, and modified through natural selection. Here, we extend this program by asking what minimal physical principles are required for adaptable life. We propose six postulates governing adaptive living systems: the existence of an entropy source, longevity of information, fast response to environmental change, repeatable operation, energetic efficiency, and networks of multiple interacting switches. These principles are introduced as a minimal foundation for biological information processing and adaptation. We examine their implications and compare them with observations across multiple levels of biological organization, including genetic inheritance, epigenetic regulation, cellular signaling, neural computation, metabolic networks, and ecological systems. The resulting framework suggests that adaptability emerges from the interplay of energy flow, information storage, information processing, and natural selection in systems maintained far from thermodynamic equilibrium. Although the proposed principles are qualitative and not yet predictive, they provide a unified perspective on the physical constraints governing adaptive behavior and offer a starting point for the development of a quantitative theory of adaptable life.