Opinion cascades and the unpredictability of partisan polarization.

"Culture wars" involve the puzzling alignment of partisan identity with disparate policy positions, lifestyle choices, and personal morality. Explanations point to ideological divisions, core values, moral emotions, and cognitive hardwiring. Two "multiple worlds" experiments (n = 4581) tested an alternative explanation based on the sensitivity of opinion cascades to the initial conditions. Consistent with recent studies, partisan divisions in the influence condition were much larger than in the control group (without influence). The surprise is that bigger divisions indicate less predictability. Emergent positions adopted by Republicans and opposed by Democrats in one experimental "world" had the opposite outcome in other parallel worlds. The unpredictability suggests that what appear to be deep-rooted partisan divisions in our own world may have arisen through a tipping process that might just as easily have tipped the other way. Public awareness of this counter-intuitive possibility has the potential to encourage greater tolerance for opposing opinions.