Saturday, March 23, 2019

Emergence and complexity in social systems

Emergent phenomena occur in social systems. For example, self-organisation, power laws, networks, aggregation/segregation, political polarisation, political revolutions...
Can lessons from condensed matter physics help at all in understanding and modeling of social systems? Can analogies from social systems help non-scientists understand some of the basic ideas in condensed matter?

In two months I am giving a  seminar in a new UQ multi-disciplinary seminar series, Futures of International Order. In preparation, I am slowly engaging with relevant literature, particularly the work of Scott Page, including his course on Model Thinking at Coursera. The NetLogo software is helpful for exploring a range of simple models.
However, before plunging in here are a few tentative thoughts of ideas that might connect with condensed matter, in the vein of reviews such as

Physics and financial economics (1776–2014): puzzles, Ising and agent-based models 
Didier Sornette

Statistical physics of social dynamics 
Claudio Castellano, Santo Fortunato, and Vittorio Loreto

Emergence occurs in systems with many interacting components. In social systems, the components are human agents. They can aggregate into emergent entities such as neighbourhoods, institutions, and communities. Associated with these new entities are new scales of size (number of agents), length, time, and connectivity. New effective interactions between entities can also emerge. Even knowing all the details of the system components and the interactions it can be very difficult to predict the properties of the whole system. Surprises are common. Humility is needed.

Qualitative changes can occur due to small quantitative changes in a system parameter.
In condensed matter examples are phase transitions between different states of matter.  Furthermore, these changes can be directly seen as discontinuities or singularities in observables. Order parameters can quantify the changes. In social systems, similar phenomena are sometimes called tipping points.

Universality versus particularity
Close to a critical point for a phase transition most of the details of the system components and their interactions do not matter. Properties such as critical exponents are independent of most details. This is wonderful for theory because one can describe large classes of diverse systems with the same model/theory and one does not have to know all the details of the system.
Similar issues of universality are also relevant when one considers phenomena at different length scales. For example, one does not need to know anything about the atoms (even their existence!) in a crystal to develop a theory of elasticity or the propagation of sound waves.
When it comes to social systems there are a wide range of phenomena that can be potentially described by the same model. For example, Miller and Page point out that the essence of the standing ovation problem is how a binary choice (sit or stand) is influenced by the behaviour of one's neighbours. This is similar to choices as to whether to join a riot, take illegal drugs, or whether to vote of political party A or B.

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