Any system that incorporates nodes connected by links can be described as a network, Professor Braha says. "The network serves as the medium on top of which various processes occur." The way that nodes are connected largely determines how a system works. "Think about how influenza spreads," he says. "Imagine a society of 10,000 people who have no social links because they live on their own. If I am the only one with the virus, clearly there is no epidemic." Then, he says, suppose people start social relationships. "For example, each pair of individuals flips a coin and decides to establish a friendship. Let's say, one in 100 folk become friends." Repeat this process for each pair, and a more connected society emerges. "But now the influenza can spread among individuals," Professor Braha notes. He cites another thought experiment, starting with a pyramid-style hierarchy. "An idea, such as 'go and protest on the street', is transmitted from a leader to followers," Professor Braha says. "In a hierarchical society like this, the speed at which information flows is limited by the chain of command – as well as the idiosyncrasies of leaders."

Information flow, he points out, rises dramatically when social links cross hierarchical and formal boundaries. "Simulations show that in an 'informal' and 'flat' form of society information spreads faster and more effectively than in one with a hierarchical backbone," Professor Braha says. Real life People in these two thought experiments were assumed to have had a similar number of friends. But in real life, the pattern of interdependence is different. "What you observe in real societies is a lopsided structure where some individuals – or companies or cities, for that matter – are a lot more connected than others," Professor Braha says.

This, he adds, leads to strange behaviours in which information is transmitted faster – and further – than expected. "As a matter of fact, it is so fast that it's difficult to contain," he explains. Civil unrest Professor Braha's research, spanning a century of civil unrest in 170 countries, reveals that social instability is similar to various physical and biological phenomena, including earthquakes, forest fires and epidemics. "Many biological systems are largely non-hierarchical and leaderless, too," says biologist James Herbert-Read at Sweden's Uppsala University. "This allows them to be robust to perturbations – take away a few individuals, whether they are cells, or individual animals, and the system still functions as a whole. Take away key nodes in hierarchical networks, and the system can fail. This makes non-hierarchical networks adaptable in the face of change." Stress

The dynamics of Professor Braha's model are based on the hypothesis that widespread unrest arises from ongoing stress, outbursts of the stress and inciting communication among individuals through non-hierarchical social networks," he says. "This leads to the spread of unrest across cities or urban areas that are connected through social and mass communication networks." According to his computer model and extensive collection of data, the shift to leaderless networks results from the fact that people have gradually become more interconnected beyond traditional hierarchies. This has led to a dramatic increase in civil unrest, similar to the thought experiment where influenza spreads faster in a more connected society. His model also shows that accumulated stresses often lead to sudden spikes in unrest. "While the rates of social, economic and political stresses in particular regions are relatively stable, accumulating stresses during peaceful times leads to periodic outburst of unrest," Professor Braha says. Example In the case of social unrest, he explains, imagine an "unrest machine" with four knobs. Even if the "stress" and "outburst" knobs were fixed, twiddling the "social networks" and "infectiousness" knobs would result in the likelihood of greater unrest.

During the recent upheaval in Brazil, the trigger for events was a peaceful rally against a small rise in bus and subway fares. Despite President Dilma Rousseff's agreement to abandon fare rises, a violent police crackdown alarmed Brazilians and brought to the surface long-standing grievances. These included nepotism and corruption, poor public transport, education and healthcare and a widening wealth gap, spurred in part by high inflation. Set against these was the high cost of hosting next year's World Cup and the 2016 Olympics. Similar to demonstrations leading to the Arab Spring, the protests across 100 Brazilian cities were facilitated largely by social media such as Facebook and Twitter. In particular, Facebook – which sparked many protests – increased its membership from thousands to hundreds of thousands. "This enabled rapid recruiting of additional protesters for propagating the Brazilian unrest," Professor Braha says.

The unrest arose, he explains, through the interdependence of closely related regions where people participated in collective protest because of long-standing grievances – and because others recently did so. "When people watch other people rioting they tend to respond similarly – even if their external conditions have not changed," Professor Braha concludes. "And protests spread across non-hierarchical social networks and from place to place." It's an interesting idea that changing the connectedness of the social network can lead to spontaneous outbursts in social unrest, Dr Herbert-Read says. "But whether we can predict when and where these spikes will occur is likely to be challenging – much like predicting stockmarket crashes and disease epidemics." The future Might the trend towards leaderless networks one day spark some form of informal and virtually spontaneous global revolt?

Some models predict extreme inequality where money flows towards a few individuals or groups in society, Professor Braha says. "And the accumulation of social and economic inequality, the failure to adapt to global resource depletion, population growth near the limits of available resources and environmental degradation are all of concern." Important advances, he says, in worldwide mobility and communication networks, and the large-scale reach of mass media would lead to a global village and the dissipation of cultural differences. "In such a highly connected society, local uprisings would tend to spread very fast across the world – resulting in global civil unrest." Links Check out the subtleties of complexity theory at: leeds.ac.uk/sociology/people/swdocs/Complexity%20Theory%20realism%20and%20path%20dependency.pdf Find out how self-organisation works at: selforganisingsystems.com/

Discover more about Professor Braha's research at: necsi.edu/affiliates/braha/dan-braha-description.htm VCAA links VCE Biology: vcaa.vic.edu.au/Documents/vce/biology/BiologySD-2013.pdf AusVELS Science: Biological sciences: ausvels.vcaa.vic.edu.au/Science/Curriculum/F-10 Please send bright ideas for new topics to pspinks@fairfaxmedia.com.au