教室里温暖宜人,萨迪斯·费区教授正忙着写板书,身后是一片笔尖勤奋地划过笔记本纸面的沙沙声、日光灯管的嗡嗡声和脚步移动声,沙滩男孩的歌声顺着敞开的窗户从院子里飘进来。“也就是说,”他继续说道,“回到过去这件事违反了因果论的原则,因此似乎是不可能实现的。”他转身面向学生,“通常我们都会用‘祖父悖论’来举例说明。”假设我找到了一种方法可以回到过去,见到了自己年轻的祖父,那么,我就可以在他还没有生下后代之前杀死他。但如果我成功了,那个穿越回过去的人又是谁呢……“ The classroom was warm and warm. Professor Sadis Fay, who was busy writing a writing on the writing board, was behind a piece of paper with a pen tip diligently striding across the surface of the notebook. The buzzing of the fluorescent tube and the movement of the footsteps moved the singing of the beach boy down. Open windows floated in from the yard. ”He continued, “ Returning to the past is a violation of the principle of causality and therefore seems impossible to do. ”He turned to face the student, “ Often we would use the ”grandfather Paradox. “” Suppose I found a way to go back and see my young grandfather, then I could kill him before he even gave birth to future generations. “ But if I succeed, who is the one who goes back through ... ”