The Guardian

11/27/2025

Small changes to the tone of posts fed to users of X can increase feelings of political polarisation as much in a week as would have historically taken at least three years, research has found.

A groundbreaking experiment to gauge the potency of Elon Musk’s social platform to increase political division found that when posts expressing anti-democratic attitudes and partisan animosity were boosted, even barely perceptibly, in the feeds of Democrat and Republican supporters there was a large change in their unfavourable feelings towards the other side.

The degree of increased division – known as “affective polarisation” – achieved in one week by the changes the academics made to X users’ feeds was as great as would have on average taken three years between 1978 and 2020.

Repeated exposure to posts expressing antidemocratic attitudes and partisan animosity “significantly influences” users’ feelings of polarisation and boosts sadness and anger, they found.

Musk bought Twitter in 2022, rebranded it X and introduced the “for you” feed, which instead of only showing posts relating to accounts users actively follow, uprates content calculated to maximise engagement.

The extent to which more antidemocratic posts make users feel greater animosity towards political opponents “demonstrates the power of the algorithm”, said Martin Saveski, assistant professor at the University of Washington information school, who, with colleagues at the universities of Stanford, Johns Hopkins, and Northeastern, produced the study published in the journal Science.

“The change in their feed was barely perceptible, yet they reported a significant difference in how they felt about other people,” added Tiziano Piccardi, assistant professor at the Johns Hopkins University computer science department and co-author of the research. “Based on US trends, that shift corresponds to roughly three years of polarisation.”

The study also found that relatively subtle changes to the content of users’ feeds can significantly reduce political animosity among Republicans and Democrats, suggesting X had the power to increase political harmony if Musk chose to use it in that way.