Elaine Hatfield is a social psychologist whose primary research focus is on relationships and love.She has focused on two types of love: compassionate and passionate. Compassionate love is marked by trust and companionship while passionate love is more physical and sexual. She (along with William Walster) developed the three factor theory of passionate love. This theory proposes that passionate love occurs with three different components. The first factor is to learn about love through the environment by examples presented by movies, books, and songs. The second factor is that a love object must be present with the third factor being a state of physiological arousal. Compassionate love develops over time and is typically longer lasting than passionate love.