Assembly Theory

Sara Imari Walker and Lee Cronin's theory that an object is its construction history. Its assembly index is the fewest recursive joining steps needed to build it from parts, reusing sub-assemblies already made; its copy number is how often it recurs. Since every step multiplies the possibilities, a high-index object found in abundance (Walker's Lego Hogwarts) cannot have fluctuated into being and is evidence of selection, which Walker locates already in chemistry. Cronin's spectrometry finding that only biological samples exceed an index near fifteen lets her treat the origin of life as a measurable phase transition and evolved complexity as a physical attribute, the basis of Size in Time and her definition of life. Bratton borrows it as the first rung of Scaffolding. Agüera y Arcas's Dynamic Stability agrees that selection precedes biology but does not require reproduction, hence their disagreement over whether a singleton Earth is alive.