On the necessity of complexity

Wolfram’s Principle of Computational Equivalence (PCE) implies that universal complexity abounds in nature. This paper comprises three sections. In the first section we consider the question why there are so many universal phenomena around. So, in a sense, we seek a driving force behind the PCE if any. We postulate a principle GNS that we call the Generalized Natural Selection principle that together with the Church-Turing thesis is seen to be equivalent in a sense to a weak version of PCE. In the second section we ask the question why we do not observe any phenomena that are complex but not-universal. We choose a cognitive setting to embark on this question and make some analogies with formal logic. In the third and final section we report on a case study where we see rich structures arise everywhere. 1 Why complexity abounds Throughout the literature one can find various different and sometimes con-tradicting definitions of what complexity is. The definition that we shall employ in the first section involves the notion of a universal computational process/device. For the second and third section of this paper we shall use slightly less formal and more relaxed notions of the word complexity. 1 a