How math can help us understand terrorist networks

Extremist groups like ISIS have utilized social media platforms to extend their global reach and message. Even with companies suspending accounts affiliated with these groups — for example, since mid-2015 Twitter has closed 125,000 — extremist groups can still be found on various social media platforms.
In two studies, published in Science and Science Advances, a group led by physicist Neil Johnson tracked the growth and decline of extremist networks on social media platforms through mathematical models typically used to map complex systems in the natural world. 
Johnson began his research by studying terrorist networks on the Russian social network, VKontakte. He says the behavior of people online can be mathematically compared to the movements of marine life or galaxies. 
“It’s very interesting,” Johnson says. “Just like in marine ecology ... fish form into groups, and they form into bigger groups, and they fragment when any predator or any sense of danger is around. There are modera