This study examines the impact of political mobilization messages on social influence and real-world voting behavior through a randomized controlled trial involving 61 million Facebook users during the 2010 US congressional elections. The results show that the messages directly influenced political self-expression, information seeking, and real-world voting behavior. Additionally, the messages had a significant indirect effect through social transmission, with the effect being greater than the direct effect of the messages themselves. The study found that the influence was more pronounced among "close friends" who were more likely to have face-to-face relationships. The findings suggest that strong ties are crucial for spreading both online and real-world behavior in human social networks. The study also highlights the effectiveness of online political mobilization and the importance of considering social influence in behavior change efforts.This study examines the impact of political mobilization messages on social influence and real-world voting behavior through a randomized controlled trial involving 61 million Facebook users during the 2010 US congressional elections. The results show that the messages directly influenced political self-expression, information seeking, and real-world voting behavior. Additionally, the messages had a significant indirect effect through social transmission, with the effect being greater than the direct effect of the messages themselves. The study found that the influence was more pronounced among "close friends" who were more likely to have face-to-face relationships. The findings suggest that strong ties are crucial for spreading both online and real-world behavior in human social networks. The study also highlights the effectiveness of online political mobilization and the importance of considering social influence in behavior change efforts.