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One of the main complexity ideas is the basic difference between the methods of explanation, which are based on a (deterministic) global parameterization of a macroscopic dynamics and the (stochastic) " multi-agent-modeling" (MAM) method.

In many physical, economic etc situations, we find it is most natural to view the system under study as a collection of elements (the agents), which interact among themselves in relatively simple ways, and (co-)evolve in time. We will call occasionally "microscopic" such a representation of the "MACRO" objects in terms of their many "MICRO" components (agents) which interact by elementary interactions (INTER).

For example:

• Animal populations (MACRO) are composed of individuals (MICRO) which are constantly born (and die), and compete (INTER) with other members of their species (for food, mates etc).
• The stock market (MACRO), is composed of many investors, each having a certain personal wealth (MICRO). The investors buy and sell stocks (INTER), using various strategies designed to maximize their wealth.

We are listing below the multi-agent MICRO-INTER-MACRO scheme of a few systems. Each scheme, lists the "microscopic" agents (MICRO), their elementary interactions (INTER) and the macroscopic emerging features (MACRO):

• Microscopic Drivers and Macroscopic Jams
• MICRO - cars
• INTER - go ahead/give way at intersections.
• MACRO - traffic flow, jamming.
• Dramas - mathematical categories endowed with dynamics
• MICRO - categories
• INTER - relations, composition laws
• MACRO - (stories) dramas
• Microscopic Concepts and Macroscopic Ideas
• MICRO - elementary concepts
• INTER - archetypical structures and thought procedures
• MACRO - creative ideas and archetypes
• Microscopic Seers and Macroscopic Sight
• MICRO - line elements, points in 2 Dimensions..
• INTER - time and space data integration.
• MACRO - 3 Dimensional global motion.
• Microscopic Draws and Macroscopic Drawings
• MICRO - line curvature, speed, discrete mental events.
• INTER - continuity, kinematics, breaks, (mind) changes.
• MACRO - shapes , representational meaning.
• Microscopic Wealth and Macroscopic Power Laws
• MICRO - investors, shares
• INTER - sell/buy orders
• MACRO - market price (cycles, crushes, booms, stabilization by noise)

The following research routine is common for most of these studies:

• modeling the system as composite of many Micros.
• simulation and visualization of the resulting model.
• identification and numerical study of the slow eveolving modes within the microscopic system.
• identification of the Macros.
• predictions based on the Macros behavior of the model.
• comparison with the experimental macroscopic behavior
• validating or correcting the microscopic model in view of the comparison.
• starting new experiments based on these results.

The use of this dialogue with an artificial system created in the computer in order to understand its large scale properties extends to systems away from equilibrium and to complex systems which are not characterized by an energy functional or by an asymptotic probability distribution.

Complexity proposes among other things to use this understanding in the task of formulating and studying Multi-Agent models for basic problems in a wide range of fields.

Next: Beyond the Soft vs. Hard Science Dichotomy
Up: Table of contents
Previous: From Reductionism to the Multi-Agent Complexity Paradigm.