arXiv subjects

Jeroen Bruggeman

Publications and source records attributed to Jeroen Bruggeman.

10 recordsLinked to original sources

arXiv2026

Intergroup violence in bursts

During intergroup confrontations, agitating stimuli such as opponents' threats and provocations can trigger collective violence, even without the usual mechanisms of ingroup cooperation, such as norms with sanctions. We examine video recordings of street fights between groups of young men. Their violence sometimes breaks out in a burst, wherein a majority of participants starts fighting almost simultaneously. At other times, only few group members participate and it takes them more time to do so. This difference in commencing collective violence can be understood by perceiving it as a collective action dilemma. We adapt an Ising model to show that the proportion of group members who cannot or do not want to contribute to the public good -- victory over opponents -- predicts whether violence takes the form of a burst or not.

physics.soc-ph↗

arXiv2026

The distribution of violent event and interevent times in conflicts

Enduring violent conflicts are interrupted by lulls without violence. Studies of interevent times found power law distributions based on coarse-grained data with a resolution of one day. Fine-grained data of violence with a resolution of seconds or shorter is rare. A mathematical theorem predicts that the distributions thereof is lognormal, not power law. However, when violent conflicts are represented as multiplicative processes and fine-grained data is used, the log normal does not fit better than the power law. Therefore, common wisdom is not refuted. Violent events, by contrast, take much energy and their durations are shorter, hence they are lognormally distributed.

physics.soc-ph↗

arXiv2024

Collective memory, consensus, and learning explained by social cohesion

Humans cluster in social groups where they discuss their shared past, problems, and potential solutions; they learn collectively when they repeat activities; they establish social norms; they synchronize when they sing or dance together; and they bond through social cohesion. A group is more cohesive if its members are closer together in their network and are bonded by multiple connections. Network proximity and redundancy are indicated by the second smallest eigenvalue of the Laplacian matrix of the group network, called the algebraic connectivity. This eigenvalue is key to explaining and predicting the outcomes of said activities.

cs.SI↗

arXiv2020

Cooperation for public goods under uncertainty

Everyone wants clean air, peace and other public goods but is tempted to freeride on others' efforts. The usual way out of this dilemma is to impose norms, maintain reputations and incentivize individuals to contribute. In situations of high uncertainty, however, such as confrontations of protesters with a dictatorial regime, the usual measures are not feasible, but cooperation can be achieved nevertheless. We use an Ising model with asymmetric spins that represent cooperation and defection to show numerically how public goods can be realized. Under uncertainty, people use the heuristic of conformity. The turmoil of a confrontation causes some individuals to cooperate accidentally, and at a critical level of turmoil, they entail a cascade of cooperation. This critical level is much lower in small networks.

physics.soc-ph↗

arXiv2020

Spontaneous cooperation for public goods

Cooperation for public goods poses a dilemma, where individuals are tempted to free ride on others' contributions. Classic solutions involve monitoring, reputation maintenance and costly incentives, but there are important collective actions based on simple and cheap cues only, for example unplanned protests and revolts. This can be explained by an Ising model with the assumption that individuals in uncertain situations tend to conform to the local majority in their network. Among initial defectors, noise such as rumors or opponents' provocations causes some of them to cooperate accidentally. At a critical level of noise, these cooperators trigger a cascade of cooperation. We find an analytic relationship between the phase transition and the asymmetry of the Ising model, which in turn reflects the asymmetry of cooperation and defection. This study thereby shows that in principle, the dilemma of cooperation can be solved by nothing more than a portion of random noise, without rational decision making.

physics.soc-ph↗

arXiv2018

The Micro Dynamics of Collective Violence

Collective violence in direct confrontations between two opposing groups happens in short bursts wherein small subgroups briefly attack small numbers of opponents, while the others form a non-fighting audience. The mechanism is fighters' synchronization of intentionalities during preliminary interactions, by which they feel one and overcome their fear. To explain these bursts, subgroups' small sizes and leaders' role, a social influence model and a synchronization model are compared.

physics.soc-ph↗

arXiv2017

Consensus, Cohesion and Connectivity

Social life clusters into groups held together by ties that also transmit information. When collective problems occur, group members use their ties to discuss what to do and to establish an agreement, to be reached quick enough to prevent discounting the value of the group decision. The speed at which a group reaches consensus can be predicted by the algebraic connectivity of the network, which also imposes a lower bound on the group's cohesion. This specific measure of connectivity is put to the test by re-using experimental data, which confirm the prediction.

physics.soc-ph↗

arXiv2013

The Strength of Varying Tie Strength

``The Strength of Weak Ties" argument (Granovetter 1973) says that the most valuable information is best collected through bridging ties with other social circles than one's own, and that those ties tend to be weak. Aral and Van Alstyne (2011) added that to access complex information, actors need strong ties (``high bandwidth") instead. These insights I integrate and generalize by pointing at actors' benefits and costs. Weak ties are well-suited for relatively simple information at low costs, whereas for complex information, the best outcomes are expected for those actors who vary their bandwidths along with the value of information accessed. To support my claim I use all patents in the USA (two million) over the period 1975---1999.

physics.soc-ph↗

arXiv2013

Network Diversity and Economic Development: a Comment

Network diversity yields context-dependent benefits that are not yet fully-understood. I elaborate on a recently introduced distinction between tie strength diversity and information source diversity, and explain when, how, and why they matter. The issue whether there are benefits to specialization is the key.

cs.SI↗

arXiv2009

Community detection in networks with positive and negative links

Detecting communities in complex networks accurately is a prime challenge, preceding further analyses of network characteristics and dynamics. Until now, community detection took into account only positively valued links, while many actual networks also feature negative links. We extend an existing Potts model to incorporate negative links as well, resulting in a method similar to the clustering of signed graphs, as dealt with in social balance theory, but more general. To illustrate our method, we applied it to a network of international alliances and disputes. Using data from 1993--2001, it turns out that the world can be divided into six power blocs similar to Huntington's civilizations, with some notable exceptions.

physics.soc-ph↗