The Physics of Causation

TL;DR

Assembly theory introduces a physical measure of causation through the assembly index, enabling a quantitative and testable definition of life and its properties within fundamental physics.

Contribution

The paper presents a novel material property-based causation measure, the assembly index, to distinguish life and its derivatives from non-living structures.

Findings

Assembly index quantifies the causal complexity of objects.

High assembly index objects indicate persistent causal mechanisms.

Assembly theory provides a physics-based framework for defining life.

Abstract

Assembly theory (AT) introduces causation as a material property and establishes a metrology for objects produced by evolution and selection. The physical scale of causation is quantified by the assembly index, defined as the minimum number of recursive steps necessary to make an object. Observing countable copies of high assembly index objects indicates a mechanism producing them is persistent, such that the object's environment constructs a memory that traps causation within a contingent chain. Copy number and assembly index together underlie a standardized metrology for detecting causation (assembly index) and contingency (copy number). These allow a precise definition of an assembly threshold that demarcates life (and its derivative agential, intelligent, and technological forms and artifacts) as structures with persistent copies in regimes of deep causal possibility. In introducing a fundamental concept of material causation to quantify and measure life, AT represents a departure from prior theories of causation, such as interventional ones, which have so far proven incompatible with fundamental physics. We discuss how AT's concept of causation provides the foundation for a theory of physics that allows precise and testable concept of "life", and in which novelty, contingency and the potential for open-endedness are fundamental, and determinism is emergent from selection along assembled lineages.