Paper on Reductionism and Emergence

There is an interesting commentary on reductionism versus emergence in today's issue of Nature:

Binder, P.-M. (2009). The Edge of Reductionism. Nature 459: 332-334.

It discusses the difference between irreducible and undecidable systems (in Wolfram's sense) and provides examples of cellular automata that illustrate undecidability despite knowledge of the simple local governing laws.

It's worth a glance.