My rating: 5 of 5 stars
Ahl and Allen's work is a monumental work that tackles the issue of observing and interpreting complex patterns not by focusing on the acquisition of data itself, but by focusing on how the observer gathers data and, in the process, affects the data itself. A system has "complexity" when its several sub-systems can be examined on different levels of granularity, some of which do not correlate well with others within the same system because of problems of physical or temporal scale.
For example, whale migration might be viewed at the level of the pod, the individual whale, or even the individual cells of a whale. Tornadoes might be viewed at the climatological level, the meteorological level, or as a series of millions of molecular vectors in space. The questions asked, data gathered, and conclusions one gathers from the data might all be valid, but might not agree with each other in a meaningful way. This is not because of any naturally-occurring essence of the observed itself, but because of the way in which it is observed. Hierarchy theory attempts to at least alert the practitioner (of whatever observational school - biology, chemistry, physics, philosophy, mathematics) to the fact that their observations must affect what is being observed. To quote the authors:
Since complexity comes from the relationships between levels, it is to be expected that complexity is not a feature of the external world. Complexity does not exist independently of an observer's questions. Instead, complexity is the product of asking questions in a certain way.
In essence, then, an observer-free observation is meaningless.
Beyond this mere proposition, Hierarchy Theory goes on to provide insights into how the observer might order observations by ordering hierarchical levels, considering necessary changes to observation levels in a nested hierarchy, filtering information, and defining the whole with surfaces.
It's been some time since I've applied these principles, in practice, but when I studied African History as a graduate student, I found these guidelines extremely helpful in determining scope and the appropriate level of temporal and/or geographical granularity for the examination of historical processes and events. This was particularly true for my Master's Thesis, which was a study of the colonial response to the Mau Mau rebellion in British East Africa. I won't bore you with the details, but suffice it to say that whenever I started to experience scope-creep, the principles I learned from Hierarchy Theory kicked in and brought me back to square one. I had to examine my examinations and "reset" to an appropriate scale.
While many of the ideas in Hierarchy Theory seem obvious to anyone who has undertaken serious academic research, Ahl and Allen's presentation collates many of the methods on which one might have accidentally stumbled in the course of observation and presents to the reader a step-by-step approach to assessing the observer's assumptions vis-a-vis observed data.
My most sincere hope is that someone much more intelligent than I am will "diff" this book against the Copenhagen interpretation of quantum mechanics. It seems to me that the dovetailing of hierarchy theory and the Copenhagen interpretation would provide some interesting grist for scaling quantum observations "up" into the classical realm or even further up into the cosmological realm. I have a hunch that such an exercise might provide great insight into the workings of the universe at the borders between the quantum, classical, and cosmological scales. Again, this would require the brains and time of someone much better endowed with both than I am. Any takers?
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