The Threshold Model – A Fundamental Organizing Principle in Physics, Chemistry, and Biology

Across physics, chemistry, and biology, a fundamental pattern repeats: systems donot change smoothly but at critical boundaries – thresholds – where the response shiftsqualitatively. This article presents the threshold principle as a universal organizing principle.A threshold is defined by a limit value for a control parameter, a qualitative change inthe system’s response, and a before/after structure. Irreversibility is discussed as contextdependent: prominent in chemistry and biology, more variable in physics. The principleis illustrated through examples from phase transitions, chemical kinetics, enzyme saturation, immune response, and information theory, including Landauer’s principle of erasure[26]. The threshold principle forms part of a triadic explanatory framework together withthermodynamics, which indicates what will happen, and the principle of least resistance(path of least resistance), which describes how it happens. Together, they constitute a modelfor change in energy-based systems, answering the questions of direction, timing, andmechanism. The question of why – in the sense of ultimate causes – lies beyond the scopeof this framework and points toward domain-specific explanations: quantum mechanical inphysics, evolutionary in biology. The principle’s status as a law of nature is discussed, andit is argued that it should rather be understood as a metaprinciple – an observable patternacross domains – than a specific physical law. The article concludes with a new perspectiveon application: threshold diagnostics, where focus is shifted from measuring the system’sresponse to measuring the control parameter driving the system toward the threshold. English translation of the Danish original DOI: 10.5281/zenodo.19249616