Mark A Bedau - Downward Causation and Autonomy in Weak Emergence (2003)

In which we are given the first serious and hopeful treatment of 'weak emergence', a term coined by Bedau some time prior to this stellar piece of work. Focusing squarely on the objectivist models of emergence (that is, those which do not rely on some subjective element of surprise), Bedau lays down a convincing argument that the ability to reduce an emergent property to its underlying parts does not make it uninteresting or insignificant.

Weak emergence sits in the middle of a trio of identified categories: "nominal emergence", which stipulates simply that a macro-level property depends on a collection of micro-level parts but cannot be held individually by these parts; and "strong emergence", which requires the existence of irreducible, supervenient macro-level properties and causal powers. Bedau makes his thoughts on strong emergence clear when he states: "Strong emergence starts where scientific explanation ends".

A phenomena which falls within the class of "weak emergence" can, given archangel-like computational powers, be derived from the network of interactions through which it emerges. However, such a network may comprise of "myriad non-linear and context-dependent micro-level interactions", making it unfeasible to forecast its outcome without simply iterating through these interactions. There is no "short-cut" derivation, to use Bedau's terminology; the extreme context sensitivity means we must simply churn through the micro-level processes until the macro-level outcome has been determined. This touches on the Kolmogorov-Chaitin notions of algorithmic complexity and incompressibility: there is no shorter way to calculate the algorithm's output than simply executing the algorithm itself.

One immediate question that surfaces is how complex this complexity needs to be. Surely some derivations are reasonably obvious, with quasi-shortcuts or broadly general solutions. Bedau addresses this by affirming a "spectrum of more or less weak emergence", with prospective properties being intractable to simulate. This fits into the intuition that there is no clear line between emergent and non-emergent properties.

We finally see how "weak emergence" tallies up with the perennial problems of causal exclusion and downwards causation. Since there is no longer the unbridgeable rift of duality that strong emergence imposes between macro and micro, the macro causal structure is equal to the aggregate of micro causal elements, and so no micro causal laws are overturned or out-prioritized. The vicious circle argument (in which a macro property can, at a given time t, theoretically affect and scoop out its own subvenient base) is not applicable because weak emergence is inherently diachronic; a macro pattern can subvert its micro constituents at time t+1, but that's OK -- this is exactly what happens in the real world (we experience neural pain as a headache, we take a painkiller, the underlying neural cause dissipates and we no longer have the conscious experience of pain).

The last worry, then, is that we are back to a plain epistemic mode of emergence: the entire causal structure at the macro level can be predicted, given knowledge of the micro-level constituents and sufficient processing time. This is true. However, given that a macro behaviour can be realised through many different routes, whole new general classes of macro entities can be created, with autonomy from particular micro pathways (and here, it's noticeable that the language switches to talking about the same "kinds of" macro behaviours). The justification is that the same process is used to justify causal autonomy between, say, chemistry and biology. This defence is only somewhat convincing, though feels like it is lacking in rigour.

As an addendum, most of Bedau's novel examples are given by way of Conway's Game of Life automata, its first major appearance in this reader. We'll be seeing more of it in the following chapters.

Sorry to all of you who have been checking back each day, only to be brutally rebuffed by the lack of any new doors. With luck, the missing days should be made up very shortly.