Researchers find possible cause for increasing polarization

Why Friending More People May Be Tearing Us Apart

Something strange happened between 2008 and 2010. Americans suddenly had more close friends than ever before, jumping from an average of two confidants to four or five. At the exact same time, political polarization spiked upward in a pattern that researchers could measure objectively across thousands of surveys. Now scientists think they know why these two trends might be connected, and the answer challenges everything we assume about social connection.

Stefan Thurner and his colleagues at the Complexity Science Hub in Vienna analyzed decades of survey data and found a troubling paradox: the more closely connected we become, the more fragmented our society grows. Their mathematical model, published in the Proceedings of the National Academy of Sciences, suggests this is not just correlation but causation, driven by the fundamental mathematics of how networks behave.

The Two-Friend Era Is Over

For generations, sociological research painted a consistent picture of American social life. People maintained roughly two close friends, the kind of relationships that could genuinely influence their thinking on important issues. That number held steady across studies for decades, a reliable constant in the shifting landscape of modern life.

Then came 2008. The researchers, tracking 30 different surveys covering more than 57,000 people across Europe and the United States, watched that number climb sharply. By 2024, the average had reached 4.1 close friendships. The shift happened fast, concentrated in just a few years around the time Facebook opened to the public and smartphones began appearing in millions of pockets.

Jan Korbel, a scientist at the Complexity Science Hub, describes the finding with a note of surprise in the published work.

“Around 2008, there was a sharp increase from an average of two close friends to four or five.”

Meanwhile, political attitudes were hardening. The team examined more than 27,000 surveys from the Pew Research Center, which has been asking Americans the same political questions since 1999. In that first year, only 14 percent of respondents held consistently liberal views. By 2017, that figure had jumped to 31 percent. Conservative views showed a similar pattern, rising from 6 percent to 16 percent. The middle ground, where people held a mix of liberal and conservative positions, was emptying out.

When Connection Becomes Fragmentation

The researchers built a mathematical model to test whether these patterns were related. What they found resembles a phase transition in physics, like the moment water suddenly crystallizes into ice. Below a certain threshold of connectivity, societies remain fluid and mixed. But cross that critical line, somewhere between three and four close contacts, and the system snaps into a new configuration: fewer groups, more tightly bound, with hostile or nonexistent bridges between them.

Markus Hofer from the Complexity Science Hub explains the mechanism in the study.

“When network density increases with more connections, polarization within the collective inevitably rises sharply.”

The logic is counterintuitive but compelling. When you have more close friends, you encounter different opinions more often. That sounds like it should make us more tolerant, more flexible in our thinking. Instead, it creates more friction. Each disagreement becomes an opportunity to retreat into groups that already agree with us. And because we have more friendship options available, we no longer need to work as hard to maintain relationships that challenge us.

Thurner offers a blunt thought experiment. If you only have two friends, you will tolerate almost anything to keep them. But if you have five and one becomes difficult, you can simply let that relationship fade. You have backups. The pressure to bridge differences evaporates, replaced by the ease of curating a network that reinforces what you already believe.

The result is not just polarization but fragmentation, a term the researchers use carefully. People do not just disagree anymore. They sort themselves into camps that barely communicate, connected only by thin threads of hostility. Democracy, which depends on all parts of society participating in shared decision-making, begins to break down when groups can no longer talk to each other.

The timing points to social media and smartphones as accelerants, though the researchers stop short of claiming direct causation. These technologies did not create the mathematical dynamics that drive fragmentation, but they may have pushed societies past the critical threshold where those dynamics take over. The phase transition was always possible. The digital age simply made it inevitable.

What remains unclear is whether this process can be reversed, or if societies that cross the threshold are stuck in their new fragmented state. The researchers suggest that learning early how to engage with different opinions and actively cultivating tolerance might help, but those are long-term strategies for a problem that crystallized in just two years. For now, we are living in the aftermath of a transition we barely noticed as it happened.

Proceedings of the National Academy of Sciences: 10.1073/pnas.2517530122