Electronic databases, from phone to e-mails logs, currently provide detailed records of human communication patterns, offering novel avenues to map and explore the structure of social and communication networks. In this paper, the authors examined the communication patterns of millions of mobile phone users, allowing them to simultaneously study the local and the global structure of a society-wide communication network. They observed a coupling between interaction strengths and a network's local structure, with the counterintuitive consequence that social networks are robust to the removal of the strong ties but fall apart after a phase transition if the weak ties are removed. The authors demonstrated that this coupling significantly slows the diffusion process, resulting in dynamic trapping of information in communities and that, when it comes to information diffusion, weak and strong ties are both simultaneously ineffective.
The images shown here illustrate the structure of the Mobile Communication Network around a randomly chosen individual. Each link represents mutual calls between the two users, and all nodes are shown that are at distance less than six from the selected user, marked by a circle in the center.