Klaus G. Troitzsch Universität Koblenz-Landau, Germany

1. Formalising the interpretation view of social interactionsFrontiers of Complexity Science and Social Science Klaus G. Troitzsch Universität Koblenz-Landau, Germany World Social Science Forum, Bergen, Norway, May 12, 2009

2. Complex systems World Social Science Forum, Bergen, Norway, May 12, 2009

3. Fields and forces World Social Science Forum, Bergen, Norway, May 12, 2009

4. Systems of systems a b g h f e d c i j k l m n Klaus G. Troitzsch: Complex Systems Simulation in Sociology

5. Micro and macro level • “sociological phenomena penetrate into us by force or at the very least by bearing down more or less heavily upon us” [Durckheim 1895] • both interpretations can be applied to • physical systems • macro cause = field, • “downward causation” = force, • micro effect = movement, • “upward causation” = field change • social systems • macro cause = “social field”, social norms, • “downward causation” = immergence, • micro effect = norm adoption, • “upward causation” = norm innovation macro cause macro effect “upward causation” “downward causation” micro cause micro effect [Coleman 1990] World Social Science Forum, Bergen, Norway, May 12, 2009

6. Micro and macro level • but the difference is • “sociological phenomena penetrate into us by force or at the very least by bearing down more or less heavily upon us” [Durckheim 1895] • in physical systems • the effect of the “downward causation” is transitory, as is the effect of the “upward causation” as there is usually no memory on either level • in social systems • the effect of the “downward causation” lasts for a long time, it changes the state of the micro entity forever (extreme path dependence of the behaviour of humans and human systems!), as it is stored symbolically in his or her memory, and the effect of the “upward causation” also lasts for a long time, as there is a long-term memory in society (folklore, libraries, codes of law …) – and this is why we sometimse observe that “the force of law is superior to the law of force” [Pierre Saré in the opening ceremony] macro cause macro effect “upward causation” “downward causation” micro cause micro effect [Coleman 1990] World Social Science Forum, Bergen, Norway, May 12, 2009

7. Interactions • the pheromone metaphor (chemical substances whose concentration gradient is observed and reacted to) • the telepathy metaphor (agents read other agents’ memories directly) • the message metaphor (messages do not necessarily express the “objective” internal state of the sender agent) World Social Science Forum, Bergen, Norway, May 12, 2009

8. Message metaphor • Software agents in simulations of economic or social processes should be able to exchange messages that hide or counterfeit their internal states. • Agents need a language or symbol system for communicating. • Symbol systems have to refer to the components of agents’ environments and to the actions agents can perform. World Social Science Forum, Bergen, Norway, May 12, 2009

9. Immergence and second-order emergence • A: “I don’t like your • smoking here, B!” • norm-invocation messages • motivate individual agents to change the rules controlling their actions • if this happens often enough, “sociological phenomena penetrate into us by force or at the very least by bearing down more or less heavily upon us” [Durckheim 1895] • and as a consequence, these norm invocations – and the resulting behaviour – occur more and more often and become a “sociological phenomenon” A: You must not cross the street when I am approaching in my car, B! • (B abstains from smoking • in the presence of A.) (B abstains from crossing the street when A is approaching with her car.) … and we have programmed something much like this in an agent-based simulation system! (not only B, but others, too, abstain from crossing streets, not only in the presence of A’s car, but in most other cases.) (not only B, but others, too, abstain from smoking, not only in the presence of A, but also on other occasions.) World Social Science Forum, Bergen, Norway, May 12, 2009

10. CSS and policy modelling • Agent-based modelling can also be applied to less simple scenarios: • emergence of loyalties within criminal organisations and collusion between criminals and their victims: the example of extortion rackets • emergence of practices in microfinance • spontaneous formation of teams according to the skills of individual members • emergence of trust in online transactions between sellers, intermediaries and buyers World Social Science Forum, Bergen, Norway, May 12, 2009

11. Can computational social science contribute to a better understanding of complex social systems? • CSS will first teach us to be modest in our promises: the complexity of our current models is still humble as compared with the complexity of real-world social systems. • Compared to equation-based and particle-based modelling, agent-based modelling as a tool for CSS has a better chance to progress beyond the limits of our current scientific understanding. World Social Science Forum, Bergen, Norway, May 12, 2009

12. Thanks for your attention! World Social Science Forum, Bergen, Norway, May 12, 2009