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Top: Gray circles show the survey-based polarization measure over time; the red crosses represent the model prediction. Bottom: Estimated average number of close friends by country and survey. The dashed line shows a logistic regression across all data points. The transition from low to high connectivity occurs shortly after Facebook became publicly accessible (vertical line I—2006) and overtook other websites in U.S. traffic (vertical line II—2010). Credit: Complexity Science Hub
Between 2008 and 2010, polarization in society increased dramatically alongside a significant shift in social behavior: the number of close social contacts rose from an average of two to four or five people. The connection between these two developments could provide a fundamental explanation for why societies around the world are increasingly fragmenting into ideological bubbles.
"The big question that not only we, but many countries are currently grappling with, is why polarization has increased so dramatically in recent years," says Stefan Thurner from the Complexity Science Hub (CSH), explaining the study's motivation. The research was published in Proceedings of the National Academy of Sciences.
The researchers' findings confirm that increasing polarization is not merely perceived—it is measurable and objectively occurring. "And this increase happened suddenly, between 2008 and 2010," says Thurner. The question remained: what caused it?
The friendship shift: From two to five close contacts
To investigate, Thurner and his team examined whether social networks had changed—specifically, whether people's close friendships had shifted. "For decades, sociological studies showed that people maintained an average of about two close friends—people who could influence their opinions on important issues," explains Thurner.
Here too, the researchers identified a striking change: "Around 2008, there was a sharp increase from an average of two close friends to four or five," explains CSH scientist Jan Korbel.
The paradox: More connection, more division
Are these two developments related? Do more close friends—and thus denser social networks—lead to network fragmentation and ultimately societal polarization?
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