  Emotions play an important role in interpersonal interactions and social
conflict, yet their function in the development of controversy and disagreement
in online conversations has not been explored. To address this gap, we study
controversy on Reddit, a popular network of online discussion forums. We
collect discussions from a wide variety of topical forums and use emotion
detection to recognize a range of emotions from text, including anger, fear,
joy, admiration, etc. Our study has three main findings. First, controversial
comments express more anger and less admiration, joy and optimism than
non-controversial comments. Second, controversial comments affect emotions of
downstream comments in a discussion, usually resulting in long-term increase in
anger and a decrease in positive emotions, although the magnitude and direction
of emotional change depends on the forum. Finally, we show that emotions help
better predict which comments will become controversial. Understanding
emotional dynamics of online discussions can help communities to better manage
conversations.
