Why is complexification time-asymmetric?

Abstract Why do order and complexity arise in a Universe obeying the Second Law of Thermodynamics? This apparent paradox is resolved by recognizing that entropy, a microscopic dissipative process, and disorder, a macroscopic process, are different, although both are directional across time. This think-piece investigates the directionality of complexification. It describes complexity using the borrowed term ‘phase space’, characterizing structures in terms of their interactions across space and time, independently (sometimes) of the underlying physical substrate. Phase space size reflects the number of available interactions, and loosely equates to complexity. Structures can pass through ‘portals’—significant interactions that change the size of their phase space. While portals can lead to larger or smaller phase spaces, it is easier to progress into a smaller space than a larger one because there are more smaller ones; a fact that becomes increasingly true as complexification develops. This asymmetry accounts for why ordered systems seem to progress more often to disorder than the reverse over local timescales. This formulation is used to examine the evolution in living things of spatial representation, memory and language, finishing with consideration of what phase space lies on the far side of the AI portal we have recently reached.