Text messages reveal the emotional timeline of September 11, 2001

The researchers took advantage of transcripts of more than 500,000 text messages sent to pagers on the day of the attacks. The transcripts were published anonymously last year on WikiLeaks. Psychological scientists Mitja D. Back, Albrecht C.P. Küfner, and Boris Egloff of the University of Mainz in Germany used software for automatic text analysis to look for words that relate to sadness (words such as crying and grief), anxiety (worried, fearful), and anger (hate, annoyed). They also noted when various events happened that day, such as the plane crashes, President George W. Bush's two speeches, and the time when American Airlines reported the loss of two airplanes.

Anger accumulated through the day. By the end of the day, there were 10 times as many angry text messages as in the morning, before the plane crashes. Anxiety, on the other hand, rose and fell through the day; 30 minutes after a stressful event, significantly more anxiety-related words appeared in text messages than 30 minutes before. But anxiety always returned to baseline levels. The data show that people did not mainly react with sadness; that may have come later, the researchers say.

The fact that anger dominated in people's immediate reactions may help explain some of the consequences of the attacks. Anger is known to make people want vengeance; this could explain the reports of acts of discrimination against Muslims in the days after the attacks, as well as the broader societal response, the researchers speculate.