A1 Extreme affective polarization

Topic

Polarization and group identity constitute the second track of Psychophysics, describing a phenomenon distinct from the previously discussed social diffusion and contagion: whereas the first track traced how content spreads through a network, this second track describes the formation of boundaries between "us" and "them" within that same network, the echo chambers that reinforce those boundaries, and the radicalization that arises from in-group affinity rather than individual conviction.

Extreme affective polarization is the anomaly describing what happens when hostility toward the out-group becomes detached from the ideological disagreement that originally sparked it: it is not merely a case of two groups increasingly disagreeing on a specific issue, but rather of emotional hostility toward the other group growing beyond what the ideological disagreement alone would explain. The variable triggering this anomaly is precisely the gap between ideological disagreement and emotional hostility toward the out-group: as long as the two remain aligned, hostility is proportional to the actual distance between the groups' respective positions; however, when the gap widens and emotional hostility vastly exceeds the underlying ideological disagreement, the conflict ceases to be primarily about the issue at hand and becomes, above all, about the out-group itself.

This anomaly is closely related to—though distinct from—the political radicalization driven by economic frustration described under "Socioeconomic Behavior" within Econophysics. While the latter stems from a gap between expected and actual mobility—channeling economic frustration into political activity—the former arises from a gap between ideological disagreement and emotional hostility and requires no economic frustration to manifest, although the two phenomena can reinforce one another when they coincide within the same population. Moreover, sustained, extreme affective polarization creates fertile ground for the deepening of the narrative fragmentation already described by Cosmovisión in *Sociophysics*: the more hostile the relationship with the out-group becomes, the less the two groups share a common field of legitimizing narratives, and the more the two processes reinforce each other.

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