Because positing them allows you explain things about the rotation of the star or the gravitational fluctuations, what have you.

因为这样假定能帮助你解释,诸如星体运行,引力波动,等现象

耶鲁公开课 - 死亡课程节选

She is also a PhD candidate in Economics and is doing research on the behavior of options prices in a phenomenon called the "Options smile," as she's smiling at me right now.

她也在攻读经济学博士学位,目前正在研究"期权微笑",也就是,期权隐含波动率微笑现象中的价格变动趋势,她现在正对我微笑呢

耶鲁公开课 - 金融市场课程节选