An Enquiry into the Recognition of the Products of Emergence

We ask how the products of emergence come to be recognised as such in simple cellular automata, and how the macro-level is distinguished from the micro-level. Taking the pattern-basis filtering of Hanson and Crutchfield's computational mechanics as our worked example, we argue that the recognition of an emergent, and with it the macro-micro distinction itself, depends on a choice of filter, and so is a relative, though not arbitrary, determination. The quasi-particles disclosed by filtering are not real in the way the underlying cells are, but substantially real: features of the macro-description rather than of the substrate. Generalising, we contend that the hierarchy of physical reality is convoluted rather than nested, that successive levels need not be composed of the entities beneath them, and that a disciplined pluralism, rather than either reductionism or an 'anything goes' relativism, is the appropriate stance. We relate the argument to recent work on weak and strong emergence, fusion, universality, interventionist causation, causal emergence, and coarse-graining as collective computation.