**
**Understanding Observed Complex Systems

– the hard
complexity problem

**CPM Report No.: 09-203**

*By: Bruce Edmonds*

Date: 22nd April 2009

## Abstract

Two kinds of problem are distinguished:
the first of finding processes which produce complex outcomes from the
interaction of simple parts, and the second of finding which process
resulted in an observed complex outcome. The former I call the
easy complexity problem and the later the hard complexity
problem. It is often assumed that progress with the easy problem
will aid process with the hard problem. However this assumes that
the “reverse engineering” problem, of determining the process from the
outcomes is feasible. Taking a couple of simple models of reverse
engineering, I show that this task is infeasible in the general
case. Hence it cannot be assumed that reverse engineering is
possible, and hence that most of the time progress on the easy problem
will not help with the hard problem unless there are special properties
of a particular set of processes that make it feasible. Assuming
that complexity science is not merely an academic “game” and given the
analysis of this paper, some criteria for the kinds of paper that have
a reasonable chance of being eventually useful for understanding
observed complex systems are outlined. Many complexity papers do
not fare well against these critieria.

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