Free Will, Theory of Mind and the Physics of the City

Free Will, Theory of Mind and the Physics of the City

Physics of the City
I recently met physicist Bruno Giorgini
and artist MariaTeresa Sartori
( who recently started an art-science residency at IMERA ( .

Bruno is one of the founders of a field called the “Physics of the City”. In 2001 Giorgini founded the Physics of the City Laboratory, CIG- Università di Bologna of which he was the director until 2007 and he still works as a researcher.

The Physics of the City studies phenomena of urban dynamics, in particular urban mobility dynamics. Mobility is considered as an individual motivation (tendency) to move on an urban topology. The urban topology is the system considered by the physics of the city and the elementary components belonging to this system have physical and cognitive properties. They are particles able to process information making the system composed by two types of microscopic dynamics: a physical one, defined by some physical process like as collisions, forces and so on: a decisional, motivational dynamics, defined by the some perceptive properties, some states of mind, memory and so on.

A major conference was held in 2005 and a special issue of the journal Advances in Complex Systems”>
has a number of interesting articles. There has been a growing research literature.

There is a recent focus on what they call ‘e-governance’ arguing that since their physical models successfully model dynamics of human movements in the cities they have studied, in a predictive probabilistic sense, this modeling can be used as a tool for people and city officials to inform the development of a city, and also the decisions of individuals.

Bruno makes a strong claim that physics can be used to understand certain phenomena in sociology; he has an unabashed confidence in the methodology of the hard sciences. At lunch today, we were discussing inter-disciplinarity and he joked that “physics is not a discipline it is a science in itself”.

Two areas of the modeling immediately raise interesting issues:

Agents that behave with a coded “theory of mind”:

Francesco Zalungo for instance develops a collision-avoiding mechanism for a system of individual agents (pedestrians) that move in a crowd trying to reach their different goal points. The agents avoid collisions on the basis of a model of the other agents’ behavior, a “theory of mind,” which is realized at different levels through an iterative process (the first level, or level 0, corresponds to ignoring the other agents’ behavior, level 1 to assuming that the other agents will ignore each other, and so on).( ). That is they model the ways individuals behave based on their individual assessment of the intentionality of the behavior of people around them.

Free Will:

In the article “The Physics of the City: Pedestrian Dynamics on the Complex Venice Network” , Elisa Omodei, Bruno Giorgini and co authors introduce the parameter : Social Temperature which models the degree of free will of the individuals: Ti is the individual \social temperature” (i.e. a measure of the attitude to freewilling change the decision). In their detailed modeling of the movement of pedestrians in Venice they adjust the parameters until the behavior of crowds matches their observations: “In order to test our model we performed virtual experiments, injecting as input the empirical data. By tuning the control parameter T, we obtained a reasonable agreement between simulations and experimental data.”

Good News; Free Will Exists

I guess the good news is that their observations require the addition of modeling of both free will and a cognitive “theory of mind” and that human behavior in city cannot be modeled accurately just as a ‘gas of particles” without such additional parameters that take into account human cognition and its effect on behaviour. They note: Last but not least, the physics of the city is essentially non-Newtonian, that is this physics does not respect the third principle of mechanics, the principle of action and reaction.”

The bad news is that with their models for free will and theory of mind they are able to replicate very well the details of human behavior, including what they call the implications of their “panic equation” : “The potential simulates a cooperative behaviour among the automata, c being the cooperation parameter. Analytical results and numerical simulations point out that if c is less than a critical value c , there exists a unique stationary solution where the population is equally divided between the two choices, whereas when c > c there exists two stationary solutions where one of the choices is preferred by the population. This means that at the critical point c chaos emerges, with possible panic insurgence.”

In a future blog I will describe the work of the artist in the collaboration Mariateresa Sartori and how her work influences and informs the scientific research that Giorgini will be doing in Marseille during their IMERA residency. They are embarking jointly on an “Atlas of the Agoras of Marseille’ with an accompanying “Theory of the City”. MariaTeresa has just finished videotaping a dozen or so ‘agoras’ or places where people congregate in Marseille. Already she has been surprised how the very different topologies of Venice and of Marseille result in different issues for her as an artist.

One Comment

  1. Roger,

    If the physics of the city is literally “nonnewtonian”, not subject to actionand reaction, then how do we explain to an urban theologist like Richard Florida, the most obvious impact of artists on creative clustering in cities like San Franc. It is said that creaticity feeds off of itself.

    Would be interested to see the artistic translation of the ideas in your posting..



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