What is Nature-like Computation? A Behavioural Approach and a Notion of Programmability

The aim of this paper is to propose an alternative behavioural definition of computation (and of a computer) based simply on whether a system is capable of reacting to the environment-the input-as reflected in a measure of programmability. This definition is intended to have relevance beyond the realm of digital computers, particularly vis-a-vis natural systems. This will be done by using an extension of a phase transition coefficient previously defined in an attempt to characterise the dynamical behaviour of cellular automata and other systems. The transition coefficient measures the sensitivity of a system to external stimuli, and will be used to define the susceptibility of a system to being (efficiently) programmed.